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Email Deliverability Audit: Definitive Guide

Today, you’re going to learn exactly how to do an email deliverability audit. In fact, this is the same process that we used to help a client uncover that 28.8% of their emails were getting delivered to the spam folder instead of the inbox:
We are going to walk you through our exact methodology in great detail (step-by-step) and by the end of the article you will come out with a clear understanding of:
Let’s dive right in!

Note: Don’t let poor email deliverability hinder your marketing efforts any longer. Try MailGenius, the ultimate solution for ensuring your emails reach the inbox every time. Send your email to a testing address given by our tool and click on “See your score”. Improve your email deliverability today.

Measure Inbox Placement Rate

You can run a detailed inboxing report using 3rd party services like GlockApps, GreenArrow, and 250ok. We personally prefer using GlockApps when running email deliverability audits for clients due to functionality and ease of use.

GlockApps works by using Seeding Addresses to test your emails. Seeding Addresses are email accounts that are set up to mirror real people. They are set up to test different types of spam filters across multiple email providers like Gmail, Yahoo, Outlook, and so on.
Here is an example of a GlockApps inboxing report where 100% of the emails reached the inbox instead of the spam folder across AOL, Apple Mail, and so on:

On the other side of the spectrum is a client of ours who had 100% of their emails reach the Gmail promo folder:

If you run a test via GlockApps and notice that a majority of your emails are going into the spam folder instead of the inbox, then it’s very likely that you have some type of email deliverability issue that is worth diagnosing.

The next step is to create a series of A/B tests by trimming different parts of the email and re-running the tests in GlockApps.

Here are some of the split tests we recommend you run that have worked for us in the past to increase deliverability:
Before running A/B tests, we recommend that you first test out a simple plain-text email via GlockApps:

If your basic plain-text email is still landing in the spam folder a large percentage of the time on GlockApps, then it’s possible that reputation systems used by Email Service Providers have associated emails coming from your domain name or IP address as spam.

Measure Domain Reputation

Domain Reputation is measured internally by Email Service Providers.

For example, as you can see in the image below, Google Postmaster Tools provides a Domain Reputation score for high volume senders:

Your Domain Reputation is measured based on a holistic understanding of every single email you’ve ever sent. It is the #1 factor that mail servers use to decide whether your message should get delivered to the inbox.
A few ways to improve Domain Reputation:
While all of these are extremely important to consider, #3 is the one you should spend the most time worrying about.
Anytime someone marks your email as spam, that’s an infraction that will massively hurt your Domain Reputation and cause email deliverability rates to plummet.

You can think of it as speaking with your insurance provider. They’re going to determine the price based on your previous driving record and any accidents you got into….. and that’s the exact same way that mail servers work. They take a look at the entire history of everything you’ve done — the amount of bounces, spam complaints, and so on.

It’s important to note that your Domain Reputation follows you no matter where you go and is independent of the tools you use. For example, switching from MailChimp to CampaignMonitor won’t make a major difference in your email deliverability rates if your Domain Reputation is low.

Tip —  Be sure to read MailTrap’s comprehensive guide to get more insight on how to measure your email deliverability rates.

Measure Sender Score

We recommend that you run a test via by submitting your sender IP address:

Your email sender reputation is like a credit score for your email marketing. Your score identifies your sending reputation and shows you how mailbox providers view your IP address.

The higher your score, the more likely your emails will reach the inbox instead of spam.
Some factors in your control that affect the Sender Score include spam complaints, industry blacklists, mailing to unknown users, mailing to spam traps, subscriber engagement, and whitelisting.

Review Blacklisting for Domain(s) and Server IP’s

Blacklists (also known as Real-time Block Lists) are updated lists that contain a set of IP addresses and domain names associated with spam.

You can run a free blacklist email test check with MailGenius to see if your domain name or server IP are listed on any significant blacklists:

Are you listed on a blacklist? If so, don’t panic… just yet. There are hundreds of blacklists and not all of them have the same effect on deliverability.
Here are some of the most widely used blacklists used by internet service providers to determine if your IP address or domain name is associated with spam:
If you are placed on any of these blacklists, improving deliverability will be an uphill battle. Luckily, each of the sites above explains the reason(s) you got listed.
If you address the blacklist provider’s issues head on and provide a valid rationale, then you can request to be delisted.
Here is an example of a blacklist removal form:
While it’s rare, we have seen companies that do not send spam still get blacklisted.

For example, if you are sending emails through a shared email service such as MailChimp or SendGrid, then other users on those platforms may have sent spam emails through a shared IP that you both use.

More commonly, we have seen cases where clients got blacklisted because they hit a spam trap. Spam traps are email addresses that are designed to seem real but have no valid user behind them.
They are usually created by blacklist and mailbox providers to serve as honeypots. Some corporations actually work in unison with blacklist providers to create spam traps using their actual company domain name.
It’s important to note that the goal of spam traps is to identify spammers via the quality of their email lists. If you are a legitimate sender, you should not expect to see any spam trap addresses on your list. That being said, you should always validate your email list before each campaign to be on the safe side.

Ensure Email Authentication Best Practices

Email Authentication functions to prove you have the authority to send emails using your domain name.

Originally, authentication procedures were created mainly for email security purposes so that emails from your domain could not be spoofed and sent on your behalf by spammers.
Over time, Email Authentication has become crucial for avoiding the spam folder and maintaining healthy deliverability rates.
We are going to dive into the 3 most important components of authentication: SPF, DKIM, and DMARC.
It can get pretty technical and requires an understanding of DNS, but it is extremely important if you want to avoid the spam folder…. so bear with me!


SPF stands for “Sender Policy Framework”. It is a DNS text record that you add through your hosting provider and it increases the likelihood of your emails reaching the inbox.
A valid SPF record will prevent spammers from sending spam from your domain. If you do not have SPF set up correctly, that signals email providers that you might not be authorized to send emails from your domain.

MailGenius will automatically check your SPF text record to ensure that it’s set up properly and your emails are authorized:

In the SPF record, you must list all the tools which are allowed to send emails on behalf of your domain. Everytime you implement or remove an email sending tool from your workflow, it’s important that you update your SPF text record accordingly.
In the SPF record, you must list all the tools which are allowed to send emails on behalf of your domain. Everytime you implement or remove an email sending tool from your workflow, it’s important that you update your SPF text record accordingly.
For example, if you use GSuite to send emails but then decide a month later that you’d like to use MailChimp, then you need to update your SPF text record accordingly to include the MailChimp servers:

v=spf1 ~all

It’s similar to setting up car insurance. You need to make sure that the designated driver list is always accurate and all the drivers are specifically authorized to drive the car.

Still confused about SPF? Check out our tool’s page to gain a deeper understanding.


DKIM stands for “DomainKeys Identified Mail”. It prevents spammers from spoofing your domain by adding a unique digital signature to your email headers.
Similarly to SPF, Publishing a DKIM text record will will reduce the likelihood of your messages being blocked or ending up in the spam folder.

MailGenius can check to see if you have a valid DKIM record and instruct you (step-by-step) on how to set it up correctly with your specific configuration:

As long as you simply understand how to set up DKIM and SPF correctly, that’s all that matters to reduce the likelihood of triggering spam filters.

If you’re curious and want to check your records or learn about how it works on a more technical level, you can visit our DKIM tool page.


DMARC stands for “Domain-Based Message Authentication, Reporting & Conformance”. It’s important to note that it only comes into play once you have a proper SPF and DKIM record set up.

DMARC enables companies to publish policies on how email providers should treat sent emails from their domain that do not pass SPF and DKIM tests (Unauthenticated messages).
Here’s an analogy to help you understand how DMARC works:
Let’s say you owned a Tesla and someone took the keys to your car and started driving. What would you want to happen? Should the Tesla instantly be shut down? Or would you allow the driver to continue using your Tesla?
DMARC works in a similar way. It decides what you want to do with unauthenticated emails (unwanted drivers).
You can set your DMARC record to have a policy of reject, quarantine, or none. A policy of none results in no action when an email from your domain fails the DMARC mechanism, enabling spoofers to send spam from your domain.

You can check if you have a proper DMARC record by running a free spam test with MailGenius:

It’s important to note that unlike SPF and DKIM text records, email providers do not factor in DMARC when it comes to email deliverability. DMARC has no positive or negative correlation with emails being sent to spam.

While DMARC doesn’t directly impact deliverability, it helps in the sense that by securing your domain, you prevent the possibility of spammers potentially ruining your Domain Reputation through spoofing.

If you’d like to learn more about DMARC, feel free to check out this resource we created.

Review Bounce Handling

One of the most important parts of the email deliverability audit is tracking how many emails bounce. A bounced message signifies that an email provider rejected the email you tried sending.
There are 2 types of bounce messages: soft bounce & hard bounce.
Soft bounces typically indicate temporary delivery issues such as the recipient mailbox being full or a server connection timeout.
Here are a few examples of soft bounce messages:
Hard bounces indicate permanent delivery issues due to non-existent email addresses or spam issues related to your IP or domain name.
Examples of hard bounce messages:
The occasional hard bounce due to mistyping the email address and missing a letter is forgivable.
However, if email service providers notice that your emails hard bounce at a high rate, they could start classifying all your messages as spam since sending bulk messages to unverified addresses is classic behavior among spammers.

Be sure to validate your emails to avoid hard bounces using an email validation service such as NeverBounce:

Review Spam Feedback Loops

According to SendGrid, if you get as little as 1 spam complaint per 1000 sent emails, then Email Service Providers will take note of that and route your emails to spam at a higher rate than previously.

Spam complaints are the #1 factor that will hurt your domain reputation and email deliverability. You want to do everything in your power to prevent spam complaints by sending relevant emails that truly add value to your recipients.

You can actually track how many of your messages get marked as spam by using Feedback Loops (FBLs).

Most Email Service Providers automatically subscribe you to FBLs that receive information from ISPs such as Yahoo, Comcast, and so on. The goal of FBLs is to gather data on the number of spam complaints you receive (among other email metrics).

For example, take a look at CampaignMonitor’s dashboard:
As you can see, the Feedback Loop tracks the number and percentage of recipients that mark your message as spam.

If you are not using an Email Service Provider, then you can sign up manually to Google Postmaster Tools as long as you send a large volume of emails and meet the requirements.

Here is an example of Google’s Spam Feedback Loop, which shows your average spam rate on a daily basis:

Review Unsubscribe Functionality

If recipients can’t figure out how to unsubscribe from your emails with ease, you increase the chances of getting marked as spam. As a result, your email deliverability rates can drop significantly.
As part of the audit, make sure that you are following these 4 best practices:
Many marketers avoid making the opt-out process simple in fear of losing subscribers. They don’t realize that the harder it is to unsubscribe, the more likely you are to get flagged as spam — and that is the worst offense with the highest impact on deliverability rates. With enough spam complaints, there can come a point where 100% of your emails do not reach the inbox.

Be sure to check if your unsubscribe functionality is set up properly using MailGenius:

Review Sending Volume & Frequency

MailChimp released an “Email Marketing Benchmarks” report so you can compare yourself with the average email campaign statistics of MailChimp users with at least 1000 subscribers.

Here are MailChimp’s average stats across all industries (Updated March 2018):
As part of the email deliverability audit, be sure to check how you stack up against the average MailChimp user.

If the unsubscribe and abuse rates are abnormally high, then that’s a major red flag and you should pause or stop your campaign. If you don’t decrease your sending volume & frequency, then you’ll have extreme deliverability issues and your Domain Reputation can drop significantly in Google’s eyes:

So, what now?
First, figure out the root cause of the problem. Why are people unsubscribing? Why are they marking your messages as spam?

There could be a lot of reasons and it depends on your specific situation. It’s possible that the content of your emails is not engaging to subscribers. Perhaps you just need to further segment your email list.

Once you fix the problem and unsubscribe/abuse rates are lowered, you can then increase sending volume & frequency without having to worry about ruining your Domain Reputation.

Review Whitelisting Process

Do you ask your new subscribers to whitelist your email address? If not, you are missing out on one of the best methods to increase email deliverability.

Email whitelisting is a quick task that you ask of your recipients to complete so that all your emails reach their inbox instead of the spam folder.

If you can get even a small subset of your recipients to whitelist your address through Gmail or other email providers, it’s one of the highest forms of engagement and will help boost your Domain Reputation and deliverability rates significantly across all subscribers.
Here is an example of a great whitelisting instructions email I received recently that caught my attention (blurred out personal information):
You can use this template as inspiration when creating your own whitelisting instructions. Feel free to get creative and incorporate GIFs, videos, and images in your email to increase the amount of recipients that take action and whitelist your address.

Inactive/Active Subscriber Segmentation

Gmail and other email providers associate low open-rates and email click-through rates with unwanted emails. If a large percentage of your subscribers are not engaging with your messages (consistently), then over time more of your emails will get routed to spam.

If you’re not sure what to classify as a low open/click-through rate, we highly recommend (once again) that you check out Mailchimp’s “Email Marketing Benchmarks” report with average statistics across all industries:
If you’re not satisfied with your email engagement rates, then you should segment your subscribers into 2 categories:
We’ve seen clients send over 100,000 emails to subscribers who haven’t opened/clicked their emails in years!
Essentially, what you’re showing Gmail’s spam filters is that hundreds of thousands of recipients do not find your emails engaging enough to interact with. In turn, your deliverability rates drop drastically.
So what’s the solution? Simply define what an “inactive subscriber” means to you and remove them from your list.
If a subscriber hasn’t opened or clicked your email in the last 12 campaigns (count-based) or 6 months (time-based), we recommend that you never email them again. Of course, you can be more/less strict with the numbers — ultimately, it’s your choice and every situation is different.
If you’re cringing at the thought of removing subscribers from your email list, you can send out one last re-engagement campaign with an extremely enticing offer in the subject line to get your email opened.
That being said, we haven’t seen re-engagement campaigns perform too well for inactive subscribers and you run the risk of hurting your overall deliverability health.

Measure Delivery Rate

Delivery Rate is the total percentage of emails that get delivered and do not get bounced or rejected by the email provider. Use an email deliverability service to test your emails to test how many land in the recipient’s primary inbox.

You can calculate delivery rate by first determining the following:

Once you have these 2 metrics, you can then use the formula below to calculate your Delivery Rate:

A good delivery rate is an indicator of the quality of your email list. If the Delivery Rate is less than 95%, that’s normally a red flag that you are not validating your email addresses.

You can use an email validation tool called NeverBounce before every email campaign:

There are 5 categories in NeverBounce:
“Accept-All” and “Unknown” results could technically still be valid email addresses since some email servers make it impossible to confirm deliverability with certain domains.

With that being said, we strongly recommend that you ONLY send emails to “Valid” email addresses and remove the rest of the categories from your email list. 

Sending emails to “Accept-All” and “Unknown” results can increase the number of bounced messages and cause your Sender Reputation to suffer. The lower your Sender Reputation, the greater the chance of Email Service Providers associating your emails with spam.
For example, if you think about it from the standpoint of Gmail Spam Filters, “Number of bounced messages” is a concrete metric that they measure. Would a “reputable sender” get 5 bounced messages per 100 emails? Highly unlikely.

Now It’s Your Turn

That’s it for the email deliverability audit process. We hope you got some value out of it!

That’s it for the email deliverability audit process. We hope you got some value out of it! Now we would love to hear your thoughts: Do you have any questions about the process? Which technique from today’s post will you implement first? Let us know by leaving a comment and don’t forget to subscribe to our newsletter!