The complete guide to email deliverability in 2026

1. Introduction to email deliverability

Sales, marketing, and growth teams are revenue drivers—and email is one of their main channels for engaging new prospects, generating revenue, and growing the business.

This playbook was developed by Amplemarket to help every sales team understand and optimize email deliverability — and unlock more business opportunities.

1.1 What is email deliverability?

Email deliverability refers to the measure of an email's ability to reach the recipient's inbox without being filtered out as spam or blocked by email servers.

It depends on various factors, including sender reputation, content quality, adherence to spam regulations, and other technical aspects.

Good deliverability ensures high delivery rates, while poor deliverability leads to emails being bounced or diverted to spam folders, hindering effective communication.

Why does it matter at the top of your funnel? Because poor deliverability can silently kill your outbound strategy. If only half of your emails reach the inbox, your chances of generating replies, meetings, or revenue are automatically cut in half—no matter how good your targeting or messaging is.

Improving deliverability can dramatically boost your outbound performance and make your revenue forecasts more realistic.

1.2 The difference between email delivery and email deliverability

Email delivery and deliverability are closely related, but they aren’t the same thing.

Email delivery simply means that your email was accepted by the recipient’s server. It’s like mailing a letter and having it arrive at the post office.

Deliverability, on the other hand, is whether that email actually reaches the inbox instead of getting stuck in the spam folder. Think of it as making sure your letter is actually placed into the recipient's hands rather than ending up in a "junk mail" pile.

1.3 Email deliverability definitions

An email bounce happens when an email fails to be delivered to the recipient’s mailbox:

• A hard bounce happens when an email address is permanently unavailable. Situations such as when there is a typo in an email address, or when someone has left a company so his/her email is no longer available are examples of hard bounces.
• Soft bounces are usually temporary. Situations including if the recipient’s inbox is full, the email sent is too large or server outages are examples of soft bounces.
• A spam bounce happens when an email fails to get delivered because it was filtered out by Spam filters existing in mailbox providers (such as Google or Outlook) or from increased cybersecurity layers set up by company's IT admins.

Mailboxes, domains, subdomains, & secondary domains

• Mailboxes: These are individual email addresses associated with a domain or subdomain, such as jane@company.com.
• Domains vs. subdomains: The main domain (e.g., company.com) is typically your primary email address, while subdomains (e.g., mail.company.com) are offshoots used to separate communication channels.
• Secondary domains: Secondary domains are entirely separate domains from your primary one (e.g., companyemail.com instead of company.com).

Reputation

Every sender’s IP, domain, and individual email address has a reputation score. We can frame a reputation as a karma points framework: 'good' behavior will give positive points, and 'bad' behavior will give negative points.

The actions of an individual sender will impact their own reputation but also the company’s domain and IP address reputation.

That’s why in Amplemarket, our team looks at deliverability collectively;  we all share the same domain reputation, so we’re all responsible for protecting it.

Let’s dive deeper into the different aspects of reputation:

• Sender reputation: This is the reputation of a specific mailbox/ email address from which an email is being sent.
• Domain reputation: The aggregated reputation of individual mailboxes. Think of it as the sum of all sender’s reputation scores that belong to the same domain. If one user is flagged, they will hurt their own reputation and the entire domain.
• IP address reputation: As with domain reputation, all users’ activity within an IP will affect the IP address reputation. The main difference is that several companies could be sharing the same IP address.

For instance, you could be sending emails responsibly and still have a poor IP reputation because of the other companies using the same platform to send their emails (i.e. Hubspot, Sendgrid, Mailchimp, etc).

Having a single dedicated IP is expensive and usually comes as an extra feature, hence most people opt to share an IP address to reduce costs.

• Temporary reputation: When too many emails are marked as spam in a short period of time, the sender could end up in “spam jail”. This will affect reputation for 48 to 72 hours of time.

The newer the domain or mailbox, the more fragile the reputation and the more important it is you pay close attention to your activity in the first weeks or months.

We’ll dive deeper into warming up newly-created mailboxes and domains late in this guide.

Calculating delivery rate

Delivery rate measures the percentage of emails that were successfully delivered to recipients' servers (not bounced), which helps you assess the health of your email sending practices.

This metric is a fundamental starting point for evaluating your email performance, as emails must first be delivered before they can be opened or generate responses.

If you sent 100 emails and 5 bounced, your calculation would look like this:

Delivery Rate = ((100-5) ÷ 100)) x 100 = 95%

What is a poor deliverability rate?

According to industry benchmarks, anything below 80% should raise some flags.

2. What influences deliverability and reputation?

2.1. Spam filtering

Mailbox providers, such as Google and Outlook, have spam filters to stop unwanted, unsolicited, or dangerous messages from reaching the inboxes of their users. These filters look at a wide variety of signals which we’ll explore below.

More and more providers are turning to AI to fine-tune their spam filters and make them faster at adapting to ever-changing spam tactics.

Spam filters also consider user input, such as when a recipient marks an email as spam.

For all these reasons, it is never possible to guarantee that no email will land in spam.

The most common reasons for emails landing in spam can be grouped into the following five main categories: š

1. Domain/mailbox technical configurations

Having an incorrect or missing configuration on an email domain (i.e. faulty email authentiation) makes it harder for your identity as a sender to be validated and can harm your reputation.

It’s crucially important that every domain/mailbox that you set up has the following authentication protocols completed:

• Sender Policy Framework (SPF)
• Domainkeys Identified Mail (DKIM)
• Domain-based Message Authentication, Reporting & Conformance (DMARC)

Without these mechanisms for email authentication, email spammers and scammers can run free, and your emails are more likely to hit filters.

Additionally, you should always set a profile name and profile picture to show there is an identity behind your domain/mailbox

2. Volume

Your email volumes can have a direct impact on deliverability, so pay special attention to:

• Unusual spikes in the activity of emails: Sending too many emails within a short period of time (and having very little activity in the remaining periods) risks triggering suspicious activity warnings.

Sending bursts of emails also increases the likelihood of multiple recipients marking emails as spam in a similar timeframe.

• Emails sent vs Emails received ratio: the lower this ratio, the better. (i.e. A ratio of 1.0 means that for every email sent there is a reply.)

A high ratio means there is low engagement with your content, which can trigger spam filters to divert your future emails due to low relevance.

The more people engage with emails from a certain sender, the greater their chances of making it to primary inboxes.

3. Email address history

If an email address has a lot of history (i.e. it was created years ago and has been used to send and receive a lot of emails) then it will likely have a stronger reputation.

On the other hand, a brand new email address will have a clean history, so it is important to build a good reputation and warm up the mailbox before starting any outbound email campaigns.

If a newly created domain/mailbox starts sending a high volume of emails in a short period of time after creation, chances are high that emails will be diverted to spam and domain/mailbox reputation adversely affected.

4. Email content

Irrelevant email content will increase your chances of landing in spam, so don’t “spray and pray”! This is why careful lead qualification and email personalization are so crucial for your deliverability.

Here are some other things to avoid:

• Repetitive content: Spam filters will catch if senders are sending a high volume of emails that look alike, so beware of reusing the same email templates ad infinitum! It s not uncommon for sales emails to look 99% alike, but this only puts deliverability at risk.
• Adding too many links, images and videos: These characteristics are typical of marketing emails, so these emails can easily be diverted from the recipient s primary inbox. Additionally, having images and videos will make emails bulkier, which makes soft bounces more likely.
• Spammy keywords: Spam filters check for certain words or phrases, so using too much spammy language (especially alongside other things on this list) raises your chances of triggering them.

Spam trigger keywords can include - but are not limited to - words like: “Free”, “Promotion”, “Buy now”, "Click Here", "100% Guarantee", “Lowest Price”, “Additional Income”, “Easy Money”....

• Complex email signatures: Adding complex signatures with HTML code, too many links or images can hinder your deliverability by making emails heavier.

5. Data quality

Data quality is an often overlooked part of email deliverability. It sounds obvious, but sellers should always be sending the right emails to the right people.

Poor email data raises the chances of emails bouncing. In turn, a high hard bounce rate will trigger suspicious activity warnings and may hurt your deliverability in the future.

When it comes to cold outbound sales, having a bounce rate below 10% is considered safe and should not hinder deliverability.

2.2. The importance of warm up

Email warm up refers to the practice of gradually increasing the number of emails being sent from a newly created domain or mailbox with the goal of building a stronger reputation with mailbox providers and avoiding spam filters.

When a new email address is created, it has a neutral reputation. From that moment onwards, every action taken will be evaluated and used to score that reputation.

Actions that look like normal, everyday activities for an email user (such as sending and receiving a handful of emails each day) contribute to a positive reputation.

On the other hand, sending a large number of emails that are ignored or marked as spam will lower your reputation.

If that reputation falls too far, then mailbox providers will no longer accept emails from that email address.

Remember that mailbox providers such as Google and Outlook are not trying to prevent legitimate businesses from communicating with relevant leads about their products or services; spam filters serve to protect their users from suspicious activities like scam, phishing and malware.

Senders with such intentions generally create new email addresses and inundate people with malicious messages.

If a newly created mailbox scales sending volume too quickly, it is actually behaving like these suspicious senders! This is why gradual warm up is key to the success of your outbound email campaigns.

2.3 Industry trends & deliverability

Many industries such as (but not limited to) pharmaceuticals, healthcare, fintech/finance, banking, government, and defence have strict regulations that block incoming emails from getting to the end user.

These are used to prevent employees from falling for phishing scams or clicking on dangerous links. These industries typically exchange sensitive and personal information via email, hence the need for extra cybersecurity layers.

Unsurprisingly, it’s not uncommon to encounter higher spam or hard bounce rates when emailing leads in these industries.

For less digitized industries such as (but not limited to) automotive, manufacturing, and traditional retail, collecting or guessing email addresses can be more challenging.

This is because is can be harder to find information on these companies online (i.e. a LinkedIn company page or an updated website).

As a result, engaging with leads in these industries can also raise the risk of more hard bounces occurring.

2.4 How email providers detect patterns & associate domains

Email providers like Google and Microsoft use advanced machine learning and AI to detect spammy behavior. They don’t just look at individual domains — they analyze patterns across multiple domains to identify bad actors.

If multiple secondary domains tied to your company start getting poor reputations (low engagement, spam complaints, bounces, blacklists), email providers may assume:

• Your entire company engages in spammy behavior.
• New domains you register are likely to be spam too.
• Even your good domains (including the main one) should be treated with caution.

This is because providers don’t just look at one domain at a time. They analyze factors such as:

• Common WHOIS data: If multiple flagged domains share the same registration details (e.g., registered by "Amplemarket Inc."), they may be grouped together.
• Shared sending IPs: If flagged domains use the same email service providers or IP infrastructure, their reputation can spill over to others.
• Email behavior similarities: If all your domains follow the same email-sending patterns (same email templates, same volume spikes, same lack of engagement), filters may treat all of them the same way.
• Linked domains in email content: If flagged domains frequently link to amplemarket.com in emails, providers may associate them together and lower trust for amplemarket.com emails too.

The "snowball effect" of a bad reputation

If enough of your secondary domains get flagged, this can trigger a snowball effect:

Stage 1: A few secondary domains start landing in spam

• Low open rates, high bounces, and complaints cause their reputation to drop.
• You switch to new secondary domains, but keep sending the same way.

Stage 2: Email providers recognize the pattern

• They notice new domains behaving just like the old ones (same templates, same IPs, same engagement issues).
• Filters start preemptively marking all new domains as suspicious.

Stage 3: Damage spreads to the main domain

• Even though the main domain isn't sending cold emails, it gets associated with flagged domains through links, WHOIS, and behavioral patterns.
• If a user receives an email from amplemarket.com and has marked similar domains as spam before, their inbox provider might preemptively mark it as spam too.

Even transactional emails (like customer support or newsletters) might start hitting spam folders.

3. Understanding email providers & IP infrastructure

For the best deliverability, Gmail (Google Workspace) and Outlook (Microsoft Office 365) are preferred options.

These ESPs have robust infrastructure and are generally trusted by email filters, giving you a better chance of reaching inboxes.

In this section, we’ll explain email providers and other infrastructural factors in more detail so you know what to be aware of when setting up your own email systems.

3.1. The difference between ESPs and SMTP providers

• ESPs (Email Service Providers): These platforms (e.g., Gmail, Outlook) manage email services and include built-in deliverability and security features. ESPs are often better for deliverability and user trust.
• SMTP (Simple Mail Transfer Protocol) Providers: SMTP providers (e.g., Microsoft SMTP Server, SendGrid) focus on sending bulk emails. While they are cost-effective for mass mail, they often carry more deliverability risks, as spam filters closely monitor them. In some cases it can be integrated with other tools.

When should you choose ESPs or SMTPs?

• ESPs: if you need a user-friendly interface, you don’t have a high level of expertise, you need email templates, automation and analytics, but you need help with deliverability.
• SMTP: If you want to send high volumes of transactional emails, you have technical expertise, and you want control over infrastructure.

In some cases, you can use a hybrid approach. You can leverage the benefits of each solution without putting all your eggs in one basket.

3.2. What to keep in mind with SMTP providers

SMTP providers might sound ideal for scaling your email blasts, but there are a number of drawbacks you should be aware if your using them:

• Transparency in IP management: When it comes to email deliverability, your IP reputation plays a massive role in whether your messages land in the inbox or the spam folder.

Be aware that many SMTP providers might operate behind a veil of secrecy, leaving senders in the dark about the health and reputation of their assigned IPs.

• Hidden IP health risks: Imagine troubleshooting poor deliverability, only to discover the issue wasn’t your sending practices but the IP you were assigned. This is the reality for many email senders who use SMTP providers that fail to provide insight into IP reputation and health.

Red flags in IP management

• No visibility into IP health: Some providers might not share metrics like complaint rates, bounce rates, or blacklist status. Without these insights, it’s impossible to determine whether the problem lies with your practices or a compromised IP.
• Stacking users on the same IP: Providers may stack multiple users on the same IP, meaning your reputation is impacted by others’ sending habits.
• Recycling problematic IPs: Some SMTPs may reuse IPs with unresolved reputation issues, leaving senders to battle poor deliverability from the start.
• Questionable IP rotation: IP rotation is a common feature touted by SMTP providers, but be aware that not all rotation strategies are created equal! We’ll explain this below.

What does "IP rotation" really mean?

Some providers claim to rotate IPs, but their approach often falls short:

• Bad IPs stay in the pool: Instead of removing flagged or blacklisted IPs, these providers simply add new IPs to the rotation while keeping the bad ones in circulation. This exposes all users to the risk of deliverability issues.
• Overflow management: Problematic IPs are often used as overflow resources, meaning if traffic spikes, emails may still be routed through flagged IPs.

Effective IP rotation involves actively monitoring and removing unhealthy IPs while maintaining a clean pool. Providers that fail to do this are setting their users up for ongoing issues.

How to spot reliable providers

A well-managed SMTP provider does more than assign you an IP and wish you luck! They actively monitor and maintain IP health, providing users with tools and insights to succeed.

You should check they offer the following:

• Daily monitoring of key metrics: Top providers track reply rates, bounce rates, spam complaints, and blacklist status to gauge IP health.
• Proactive communication: Providers with strong reputation management flag potential issues early and provide actionable recommendations to fix them.
• Dedicated IP support: High-quality SMTPs offer dedicated IPs for users who need complete control and transparency over their sending infrastructure.

With increasingly sophisticated filters from providers like Google and Outlook, relying on outdated or opaque SMTP practices is no longer an option.

Being successful in building, sustaining, and troubleshooting your email strategies requires you to have access to actionable insights, proven reputation management, and reliable infrastructure.

If you’re opting to use an SMTP provider, be very careful! Avoid providers that keep you in the dark about IP health, recycle problematic IPs, or offer incomplete rotation strategies.

Scaling your outbound email volumes quickly might sound like a good idea, but it’s not worth damaging your deliverability (and pipeline) in the long term!

4. Amplemarket & email deliverability

Amplemarket offers a range of reporting and services to help users navigate, understand, and optimize their email deliverability, and in so doing help in maximizing value for their businesses.

In this section we’ll dive deeper into practical tips and tools you can implement to improve your deliverability.

4.1. Domain Health Center

The Domain Health Center allows our users to analyze the health stage of each of their individual mailboxes.

To view their Domain Health Center data, users can follow these steps:

1. Sign into the Amplemarket app
2. Click “Domain Health Center” in the left sidebar

Here’s how to read this report:

• Last 7 days: This shows the open rates and the number of emails sent in the last 7 days. You can sort by open rate or number of emails sent to prioritize those that require most attention.
• Volume: This column shows the outbox-to-inbox ratio, i.e. the ratio of how many emails are being sent versus how many are being received. A ratio of 1.0 means that for email that is sent, there is one email received.

When using mailboxes to run email outbound campaigns it is common to have a ratio > 1.0. Our advice is that you try to keep the ratio below 4.0 - which means that for every 4 emails sent there is 1 email received.

Mailbox info: This section combines a number of fields related to the mailboxes' authentication, identification and age:

• Authentication: View status of your SPF, DKIM, and DMARC domain authentication.
• Spam lists: The number of spam lists each mailbox appears on.

Also known as blacklists or block lists, spam lists are real-time lists that identify IP addresses or domains that are known to send spam. They’re used by organizations like internet service providers (ISPs), free mailbox providers, and anti-spam vendors to prevent spam from coming into their systems.

One common reason for appearing in one of these lists is if you’re using a shared IP that has been marked as spam in the past.

Featuring in one list is not a problem. However, if mailboxes appears in 2 or more spam lists, users should contact their email provider (i.e. Google or Outlook) and request a new IP.

• Profile Name/Profile Picture: This column shows whether mailbox owners have completed all the information on their profile. This enables prospects to preview the sender name and picture before opening sales emails, which makes your outreach look more authentic and human

• Age: The 'younger' the mailbox, the greater risk of having emails landing in spam. Mailboxes aged less than 2 months should not be sending high volumes of emails.

4.2. Amplemarket lead status

Hard bounced

Leads are classified as “Hard bounced” in Amplemarket when the email does not make it to the end user because we have the incorrect email information for this lead.

The wide majority of bounces in Amplemarket come from incorrectly guessed emails.

When new leads enter our database, we leverage the online information available for those leads to try to find an email address that belongs to them. Once we find an email address, we validate it by sending it a virtual ping and mark it as “Verified” in your lists:

There will be cases when the email address will not be validated, but we are still confident it belongs to the leads being sequenced. On these occasions the email will be entered as “Guessed” email.

Leads are classified as “Spam bounced” in Amplemarket when the email does not make it to the end user because it is being sent to spam.

This may be due to email deliverability issues or due the strictness of the end user’s email settings; sometimes emails are blocked regardless of their content.

You can also filter contacts by Status using the available filter options on the right side of the Contacts Tab (left).

4.3. Amplemarket email Deliverability Booster

The Deliverability Booster is Amplemarket’s mailbox warmup service that helps you build, protect and optimize your email deliverability. It works by automatically starting and replying to multiple threads on your behalf in order to boost your mailbox/domain reputation. You can use the Deliverability Booster to:

• Build reputation for recently created Domains/Mailboxes: Warmup is a safe way to start building a good domain reputation from scratch.

Recent created domains/mailboxes are more exposed to deliverability problems because they lack history or reputation. The automatic threads controlled by the Email Deliverability Booster will show to mailbox providers there is activity happening in that mailbox.

• Protect and maintain reputation for older domains/ mailboxes: Warm up helps even out your mailbox sent-received ratio alongside your outbound sequences.
• Damage control for domains/mailboxes flagged as SPAM: Email warm up (alongside other deliverability best practices) can help you recover your domain reputation faster in case your domain/mailbox is flagged as spam.

Important

Using Amplemarket’s Deliverability Booster feature does not eliminate the need to gradually increase the number of emails being sent from a newly created domain or mailbox!

Amplemarket can help accelerate the warm up period and strengthen domain/mailbox reputation, but domain/mailbox owners are still accountable for scaling volume in a responsible way.

4.4. Amplemarket (basic) dynamic fields

Dynamic fields are the values Amplemarket uses to tailor your outreach to individual prospects by automatically looking up specific data.

You can use dynamic fields in your sequences by simply surrounding the field name in {{ }}. Examples include {{first_name}}, {{company_name}}, {{title}}, etc. This will be replaced by the value that was provided for the lead.

For example, if a lead has "John" as the first_name field then {{first_name}} will be replaced with John.

Dynamic fields can help you optimize your deliverability by varying your content at scale.

More importantly, they allow for better personalization in your emails, which increases the likelihood of engagement.

4.5. Amplemarket (advanced) dynamic fields and liquid syntax

Advanced dynamic fields, also known as liquid syntax, allow you to format and personalize in a much more strategic way compared to basic dynamic fields.

Liquid syntax enables you to apply logic to your email templates by using conditional tags [if/else] to accommodate multiple messages within a single template.

Heres an example of liquid syntax being used to create different messages for leads with different job titles:

{% if title contains "VP" or title contains "Vice President" %}

We’ve helped VPs such as yourself... (This is the value proposition for VPs)

{% elsif title contains "Director" %}

We’ve helped Directors such as yourself... (This is the value proposition for Directors)

{% elsif title contains "Manager" %}

We’ve helped Managers such as yourself... (This is the value proposition for Managers)

{% else %} We’ve helped sales teams... (This should be a generic value proposition for all that do not fit the criteria)

{% endif %}

Not only does using liquid syntax mean your leads receive highly personalized messaging; it will also ensure you are rotating your content at scale and not sending the same exact message to hundreds of leads.

For this reason, liquid syntax is one of the best tools Amplemarkets users can leverage to optimize their email deliverability through content.

You’ll find several dynamic statements ready to use in your Amplemarket dashboard.

You can check them by clicking on the “Dynamic Fields” button when creating, launching or editing an email message in one of your sequences. If you have any questions, do not hesitate to reach out to support@amplemarket.com.

4.6. Amplemarket email placement test & mailbox selection

In part 6 of this guide, we explain how you can manually test if your emails are landing in spam.

The good news is that if you use Amplemarket, this will automatically be done for you on a weekly basis! Email Spam Check tests have two possible outcomes:

• Healthy mailbox: Your mailbox is healthy, and emails are landing in the recipient's inbox folder.
• Unhealthy mailbox: Your mailbox is not healthy, and emails are landing in the recipient's spam folder.

From this, you’ll be advised when scheduling emails as to which mailboxes are in prime condition for outbounding.

If your mailboxes are at risk, you’ll be advised to rest and re-warm them over a period of time.

You can learn more about Amplemarket’s Email Spam Checker here.

4.7. Automated mailbox rotation with Duo Copilot

Users of Amplemarket’s AI copilot, Duo, can automate their mailbox rotation!

Duo Copilot generates bespoke sequences for individual leads according to your chosen intent signals.

With dynamic rotation turned on, Duo will cross-check the health of your mailboxes per your Domain Health Center and will decide which mailbox to initiate your sequence from.

In other words, you can fully automate your email outreach without worrying about overloading individual mailboxes!

5. Best practices to optimize deliverability

The most crucial thing when it comes to optimizing your email deliverability is to protect your domain and mailbox reputation. Here are some of the most important best practices:

5.1. Set up your subdomains

To recap, subdomains allow you to build a sender reputation independently from your primary domain, making it easier to monitor and optimize your outreach.

They operate as offshoots from your primary domain and allow you to set up more mailboxes to spread the load of your emails.

Here are some top tips to make sure you set up your subdomains for success:

• Own your own mailboxes!

If possible, set up and manage your own mailboxes directly through reputable providers like Google Workspace or Microsoft Office 365.

While resellers may offer cheaper mailboxes, they often house multiple domains in the same workspace or tenant, which can impact your deliverability if other users have poor sending practices.

Additionally, cheap reseller accounts may be flagged by Google, which could place your mailboxes under closer scrutiny.

• Build with scalability in mind

For large audiences, we recommend setting up multiple domains and mailboxes:

• If you’re reaching a large target market (200,000+ people monthly), set aside time for setting up and warming up multiple domains and mailboxes. Don’t dive straight into high volume outbound!
• 5–10 domains with 2–3 mailboxes each on providers like Google or Microsoft.
• It’s important to control your email volumes even if you’re using multiple mailboxes and multiple domains. We’ll explain this in more detail below.

Pitfalls to avoid with subdomains

Subdomains can still cause deliverability problems if they’re not managed correctly. Some common issues to avoid are:

• Hiding identity: Avoid masking your primary email address with an alias on the subdomain. ESPs tend to view this tactic as suspicious.
• Improper DNS configuration: Ensure SPF, DKIM, and DMARC settings are correctly configured for each subdomain. Misconfigured DNS can lead to deliverability issues and even security risks. We’ll go over these technical configurations in more detail below.
• Overly aggressive sending: Sending too many emails too quickly from a newly established subdomain is a red flag to spam filters. Stick to your gradual warm-up plan to prevent this.

5.2. Set up the right technical configuration

a) Authentication

Ensure email domain and mailboxes are properly authenticated for in terms of Sender Policy Framework (SPF), Domainkeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting & Conformance (DMARC).

For Google users:

1. Set up SPF
2. Set up DKIM
3. Set up DMARC

For Exchange users:

1. Set up SPF
2. Set up DKIM
3. Set up DMARC

b) Custom domain tracking (optional/recommended)

By default, email sequencing tools use a shared domain to track all email opens. While this provides immediate stats, it can impact the deliverability of your emails.

Set up a custom tracking domain to ensure deliverability and reputation are entirely under your own control. Check out detailed instructions on setting up a custom tracker in Amplemarket.

While open tracking provides valuable insights, the tracking pixels used can sometimes trigger Email Security Gateways, particularly in industries with heightened security measures (like finance, healthcare, or government).

These security systems may automatically quarantine emails containing tracking pixels.

If you're targeting prospects in security-conscious industries, consider:

• Using reply rate as your primary engagement metric instead of open rate
• Disabling open tracking for specific high-security segments of your audience
• Creating separate sequences without tracking pixels for prospects in these industries

This approach may result in fewer deliverability issues when reaching out to organizations with strict email security protocols, and reply rates often provide a more meaningful measure of genuine interest anyway.

c) Mailbox setup

To make mailboxes look authentic, remember to complete all the information on their profile including your name and a profile picture so your prospects can see the preview before they open your emails.

5.3. Manage volume appropriately

It’s key keeping your volume of emails sent consistent by avoiding spikes in activity.

• Don’t overload your mailbox: Keep an eye on your send volume, paying attention to both new prospects and the rest of your existing sequence follow-ups.

You should try to keep your overall send volume to at most 150-200 emails per mailbox per day (ideally less). Of course, the maximum number of emails you can send per mailbox per day will depend on your mailbox reputation.

• Create new mailboxes/domains to spread volume: You can manage your reputation health by using multiple mailboxes under the same domain, e.g.: john@company.com, john.doe@company.com.

This allows you to distribute your sending volume between multiple mailboxes instead of overloading one.

Another thing to be aware of is that each ESP has its own limits to prevent spam and ensure high-quality user experience:

• Gmail allows up to 500 emails per day for standard accounts and 2,000 for Workspace users.
• Office 365 caps at 10,000 per day but with stricter hourly and per-minute restrictions.
• Other SMTP providers like SendGrid or Mailgun may have different caps, but using these bulk providers for cold email can hurt your deliverability.

But here’s the catch: Just because an ESP allows hundreds or thousands of emails doesn’t mean you should aim for those limits in cold outreach. Cold emails are unsolicited, and to keep your emails out of spam, it’s crucial to mimic natural, human email behavior.

5.4. Improve & protect sender reputation

Here are a few tips on maximizing your sender reputation:

• Warm up recently created mailboxes: Warming up a mailbox is the equivalent of consolidating its reputation by adding high-quality volume and engagement. A proper warmup process is absolutely essential to build a stronger email reputation in the long run.

While warming up, your engagement rates will be strong. However, once you start sending cold emails, anticipate some decline due to spam reports. Gradual volume increases will minimize risk.

• Increase your engagement rate: Add different types of activity to your mailbox in order to maximize the engagement rate and increase the number of non-sales activities. For example, you can exchange emails with colleagues, customers, friends, and subscribe to forums and daily newsletters.
• Monitor the quality of engagement: This is especially important if you use your mailbox mainly for sales emails; if you have a lot of prospects replying as Not Interested, or asking to Stop or Unsubscribe, take it as a sign you need to review your lead generation process and email templates as quickly as possible.
• Unspam your emails: When conducting sales email outreach, it's normal to have a number of emails marked as spam.

To help curb this, you can periodically send emails to personal email addresses (@gmail.com, @yahoo.com, @outlook.com...) and have the recipients mark emails as not spam if they find your email in their spam folder.

5.5. Improve & protect domain reputation

• Warm up recently created domains: It used to be possible to create a new domain and immediately start sending hundreds of sales emails.

This type of behavior is no longer tolerated and domains with poor history will be marked as spam… fast!

For every new domain you create, make sure to warm it up for at least 4 weeks before you start sending any outbound emails.

• Make sure all your mailboxes follow deliverability rules: The best practices listed in this guide should become your new standard. Don’t forget to make deliverability an essential part of onboarding and training programs for new sales team members

5.6. Avoid the "toxic domain network" effect

In part 2 of this guide, we mentioned how damage to one area of your domain reputation can cause a snowball effect across all your infrastructure.

Here’s how to prevent problems from spiralling out of control:

Diversify your sending infrastructure

• Avoid putting all secondary domains under the same Google Workspace or Microsoft 365 account.
• Use different email providers for some domains (e.g., mix in SMTP providers)
• Spread sending across multiple IPs to reduce cross-contamination of reputation.

Slow, controlled sending & warm-up

• Don't just swap to a new domain and blast emails — ramp up gradually.
• Keep sending patterns as human-like as possible (avoid sending hundreds of emails at once).

Improve engagement and avoid spam complaints

• Focus on high-quality targeting and personalization to reduce spam reports.
• Monitor reply rates, open rates, and complaint rates — stop using any domain with high spam complaints before it becomes toxic.

5.7. Optimize your email list data

You can have the best technical configuration in the world and still find your campaigns falling flat if you don’t have reliable email address data!

Remember that poor data leads to more bounces, which will cause more damage to your deliverability — not to mention the fact that you’re losing out on potential revenue everytime you send an email to a dud lead.

Here’s are some tips for data management that will give your campaigns the best chances of success:

• Beware of buying leads lists from websites: Many lead-selling websites have low-quality or outdated information. Trusting these lists can lead to high bounce rates and spam complaints.
• Limit outreach to no more than 3 per company: Avoid reaching out to multiple people in the same organization. Targeting too many individuals can trigger spam filters.
• Focus on business accounts: Send emails only to business accounts, ideally from the same ESP (email service provider), for optimal deliverability.
• Use only valid email addresses: Regularly clean your lists to remove invalid addresses and reduce bounce rates. Tools like Amplemarket offer automated email verification mechanisms that will validate old records or fill gaps in your CRM.
• Segment your list for relevance: Segment your contacts by job title, company size, industry, or other relevant persona criteria. This keeps your messaging focused and reduces the chances of triggering spam filters.
• Monitor spam complaints and bounce rates: Keep an eye on these metrics. High bounce rates or complaints can harm your domain’s reputation over time.

5.8. Optimize email content

Personalization is key. Content optimization starts with an effective lead qualification process and in bringing variability to sales motions.

• Refine your lead generation process: Try to ensure you’re reaching out to the right people to maximize your reply engagement. You should also make an effort of reaching out at the right time - when prospects are more likely to buy - to build a positive deliverability feedback loop.

If you are using Amplemarket, you can leverage highly relevant signals like Job Change Alerts, Competitive Intelligence, and Social Prospecting (and much more) to target your highest priority prospects.

• Keep your sales outreach varied: Avoid using the same template for months on end; spam filters will pick up on content that has been flagged elsewhere and harm your deliverability. Email templates should be periodically reviewed to avoid this issue.
• Avoid excessive links, images, or videos: Your goal is to encourage prospects to reply, not just click. You should first focus on getting more replies to increase your sender/domain reputation, then it will be easier for you to share links, images, and video without hitting spam filters.
• Avoid spammy keywords: Avoid using too many spamtriggering words like “Free”, “Promotion”, “Exclusive” etc.; remember that spam filters are trained to identify these words and phrases.
• Avoid excessive formatting: Try not to use too much special formatting such as bullets, bolds, sentences in different colors, fonts and sizes. Your sales emails should be as conversational as possible.
• ‍Simplify email signatures: Avoid using complex HTML signatures. In the case of signatures, less is more. Stick to plain text only, with your name, and (at most) 1 or 2 different links (e.g.: company website, LinkedIn or other).

5.9. Consider Using Sender Aliases — Wisely

Email aliases are alternative email addresses that point to a primary email account. They allow users to receive emails sent to different addresses within a single inbox. For example, if your primary email is john@company.com, you might set up aliases like support@company.com or sales@company.com, all of which redirect to john@company.com.

Where you can benefit from using aliases

• Multiple roles in a company
  • Organizational efficiency: If you handle multiple roles within your company, email aliases can help segregate communications for each role. This keeps your inbox organized and ensures that relevant emails are easily accessible.
  • Professionalism: Using role-specific aliases (e.g., hr@company.com, marketing@company.com) can present a more professional image to your clients and partners.
• Keeping former employees' contacts
  • Continuity: Maintaining aliases for former employees' email addresses (e.g., jane@company.com) ensures that important emails are not lost. These emails can be redirected to a current employee's inbox for follow-up.
  • Transition: This helps during the transition period when an employee leaves, ensuring that ongoing communications are not disrupted.
• Legal and working option for 'Do Not Reply' emails
  • Compliance: Some communications, like automated notifications or transactional emails, should not accept replies. Using aliases like noreply@company.com ensures compliance with this practice while maintaining professional standards.
  • Clarity: It makes it clear to recipients that the email address is not monitored for responses.

Why email aliases can damage your deliverability

• Spoofing and spamming risks: Using aliases across multiple domains can raise red flags with spam filters. This practice is often associated with spoofing and spamming, leading to deliverability issues.
• Deliverability scores: Spam filters may lower your deliverability scores when they detect multiple domains with aliases as this is commonly associated with malicious activity.
• DNS scrutiny: Automated outreach campaigns using aliases can bypass DNS checks, raising red flags with spam filters that rely on DNS for validation.
• Transparency: ESPs can detect the origin of aliases, making it easy to see through attempts to hide identity. This practice can decrease open rates, conversions, and increase complaints.
• Trust and Compliance: Using aliases to hide identity is rarely justifiable and can lead to violations of email compliance rules. This can result in long-term damage to your sender reputation.
• Fixing Sender Reputation
  • Trying to fix a damaged sender reputation by using aliases can backfire. ESPs can see behind the alias and may view such actions as deceptive, leading to further reputational harm.
  • This may lead to permanent deliverability problems, making it harder to rebuild a positive sender reputation.

5.10. Protect IP address reputation

• Monitor your deliverability across different platforms: Pay attention to which platforms you use to send emails (not only for sales but marketing, too).

IPs are usually shared across multiple domains. If you are setting up a new IP you should make sure you create a dedicated IP for your company’s exclusive usage. This way, you can have complete control over its reputation.

5.11. Sign up for Google Postmaster Tools

Keep an eye on your spam delivery rates:

• Email Service Providers like Google use Google Postmaster Tools to measure your SPAM rate. Fortunately, since you can access this yourself, it’s possible to have full visibility over your SPAM complaints and avoid any nasty surprises!

On logging in, you may find that you don’t have enough data to track, in which case you shouldn’t be running into problems. If your spam rate climbs above 0.3% for a sustained period, expect to see your deliverability issues increase for Google recipients.

6. Deliverability troubleshooting

6.1. Discovery

Once you understand the factors that affect your deliverability, you can kickstart your email troubleshooting by answering relevant questions individually or collectively with your team:

6.2. Assessment

Having answered the above questions, you should have a better idea of what’s affecting your email deliverability.

The good news is that if you apply the best practices in this guide, you’re on the right track to improve your email reputation.

The next step should be understanding what to prioritize to start fixing your email deliverability issues.

Amplemarket has developed this Email Deliverability Assessment Framework to help all Amplemarket users prioritize their actions to recover reputation faster.

How to use the Assessment Framework

In this framework you will need to assess three important dimensions:

• Verify all technical configuration of your mailboxes
• Analyze volume of emails sent and trends of open rates
• Review the content of your emails

You will color-code each aspect of the above dimensions to prioritize areas of highest concern:

• Red: Factors that pose the highest risk to your reputation. You should prioritize and fix everything in red ASAP.
• Yellow: Factors that may not be the main reason for deliverability issues but may be contributing factors. Turning these green green can contribute to a faster recovery of your reputation and help prevent email deliverability problems in the future.
• Green: Things that don’t require further action or intervention.

If you’re an Amplemarket admin user, you complete the assessment for your entire team.

Alternatively, you can share this template with your team members and have everyone complete their own email deliverability self assessment.

As previously mentioned, if everyone shares the same domain reputation, everyone is responsible for protecting it!

6.3. Test if your emails are landing in spam

The most effective way to test whether your emails are hitting spam is to use the mailbox in question to send emails to a variety of inboxes using different email providers. This can be done manually, i.e. creating a new email address (like a new @gmail.com account).

You then check where your emails are landing for each recipient address.

Some things to bear in mind:

• Deliverability issues can be specific to an mailbox provider - i.e. you might be having issues with Gmail but not with Outlook.
• Ideally, you run multiple test for each provider; it’s not uncommon to see a fluke where one of message lands in spam but the rest go straight to inbox.
• You might get different results depending on where you send the email from (e.g. via Gmail Compose vs Amplemarket).

There are small differences that can account for this, including the fact that Amplemarket adds an open tracking pixel which can cause your emails to end up in spam.

This is why we recommend to users setting up their own custom tracker to track email opens.

• If your messages land in spam, it is important you mark them as not spam! You can do this via the spam folder. It is also important you reply positively to those messages.
• Learn how to unspam on Gmail here.
• Learn how to unspam on Outlook here.
• Amplemarket will automatically spam-test your mailboxes every week! Learn more here.

6.4. Damage control: spam jail cases

When too many of your emails are marked as spam in a short time, your domain or IP can suffer a temporary reputation penalty — often referred to informally as “spam jail.” This isn’t always a full block, but it can result in:

• Throttling or deferrals by inbox providers
• Severe inbox placement issues (emails landing in spam)
• Temporary inability to reach recipients, especially at providers like Gmail or Outlook

What to do if you're in spam jail:

• Pause all outbound for all “at risk” mailboxes until they pass the spam tests. This gives reputation systems a chance to reset.
• Monitor inbox placement and reply rates during this time. A return to normal engagement can indicate improvement.
• Don’t send to your entire list at once when restarting. Warm up your volume slowly, starting with your most engaged users.
• Check your technical setup. Confirm that SPF, DKIM, and DMARC are properly configured and that your sending domain hasn’t been blacklisted.
• Review your recent content and targeting. High complaint rates often come from irrelevant or overly aggressive messaging.

If problems persist beyond a few days, you may be facing a broader deliverability issue that requires a more structured recovery plan.

7. Conclusion

Email deliverability remains one of the biggest and most overlooked issues in outbound sales. Throughout this playbook, we've explored email reputation in depth and shown how critical it is to deliverability success.

By implementing the right strategies and committing to continuous improvement, sales teams can significantly enhance their success rates. To stay ahead in this dynamic environment, sales teams must remain vigilant, proactive, and well-informed on current best practices:

• Recently created domains and mailboxes must be properly authenticated and warmed up to build stronger reputations in the long run.
• Sellers should refrain from sending the same exact message to hundreds of leads over and over.
• 'Spray and Pray' is not the way. Lead qualification and content personalization should be a priority to craft relevant and engaging content for recipients.
• Recognize that mailbox providers' spam filters are evolving rapidly and becoming smarter everyday due to the advanced capabilities of AI.

Remember, optimizing email deliverability should be a team effort, because everyone is sharing the same domain reputation, so everyone is responsible for protecting it!