How to improve domain reputation for better email deliverability

Domain reputation is something you earn over time. It can’t be artificially built overnight and isn’t derived from a single email going to spam or the inbox: instead, it’s based on the long-term state of your infrastructure and the consistency of your sending practices and content. 

There are several things you can do to iteratively assess and improve your domain reputation, which in turn should lead to improved email deliverability.  

Domain reputation and deliverability, explained #

Domain reputation is the opinion receivers—including mailbox providers and anti-spam services—have of your domain, which helps them decide if your emails should make it to a recipient’s inbox instead of being rejected or ending up in a spam folder. It's a lot like the reputation we build as people: it’s affected by what you’ve done in the past and who you’re associated with. 

The reason it matters is because your domain’s good reputation increases the deliverability of your emails.

Unlike IP reputation (more on this in a second), your domain reputation is portable. That means you could add new IPs, you could move IPs, you could send mail from different systems, even different ESPs—and you’d still enjoy the benefits of your good reputation.

But if your domain reputation is low, you’re at a higher risk of having your emails classified as spam. That’s why it’s important to check it regularly and fix all issues that may weaken it before you start any proactive outreach.  

1. Poor IP Reputation can lead to poor domain reputation #

IP reputation and domain reputation are two different concepts, but they can affect each other. Imagine you’re sending from an IP with low reputation: all emails sent from that server will be at risk of not being delivered; if you switch to a different IP with a high reputation, the chances of those same emails reaching the inbox improves. 

Except for this: if your domain reputation is high, but you switched to a provider that has a low IP reputation, then you're at risk of having lowered your domain reputation. And once your domain reputation is low, having a high IP reputation won’t be of much help.

Something worth remembering: 

  • Domain reputation is unique to your domain, regardless of the IP you’re sending from.
  • IP reputation is tied to the specific server you’re sending from (you can send from a dedicated IP or a shared IP)
  • Your IP reputation can help or harm your domain reputation. 
  • ISPs take into consideration your IP and domain reputation as separate functions. 

2. Email content can lead to spam and deliverability issues #

Content plays a role in whether or not an email gets delivered to the spam folder, but it also can affect your domain reputation. Transactional emails can easily be flagged as spam for having lots of exclamation marks or attention-getting subject lines that make an ISP suspicious. Here are a few helpful resources that can help improve the content on your emails: 

Postmark Spamcheck tool
Postmark Spamcheck tool

How to build and improve domain reputation #

Domain reputation is earned over time thanks to all the factors we just considered—IP reputation, infrastructure, content, etc.—which collectively paint a picture of your domain to ISPs.

Whether your domain is new and has no reputation or has existed for a while with a low reputation, 
there are a few things to keep in mind when building your reputation:

1. Domain warmup #

Warming up your domain is just as important as warming up your IP. This is because most ISPs are shifting to use domain reputation for most filtering decisions. 

But how do get ISPs to trust you when you don’t have a history of sending email? No history means no reputation and there’s no reason to trust your emails ISPs don’t know what to expect from you. What can you do?

If you’re working with a new domain start by sending small amounts of messages to your most engaged recipients. This high-engagement percentage builds your domain reputation much more quickly, allowing you to later send more messages that are less engaged without much penalty. You want to have a consistent process so that ISPs don’t become suspicious and flag your domain.

2. Domain classification #

When you registered your domain, you were likely asked to classify it to a specific industry. It’s important that the types of emails you send are consistent with the industry you selected. 

For example, if your business is classified under the dating category but you’re sending emails related to computer software, then that would be inconsistent with the selected domain type. As a result, ISPs may flag your domain.

Email consent is another aspect of domain classification that can’t be overlooked. If someone signs up to hear about events at local bars and restaurants, but later you send them a message selling wines and beer gadgets, you've lost that consent. Your described industry and content is so important and if you need to expand or change what you offer, make sure your domain registration and customer subscriber permission is updated.

3. Using subdomains #

When it comes to email deliverability, subdomains carry a lot of weight. Using a subdomain rather than your company’s top-level domain will provide easier reputation tracking because its separate from other domains and subdomains being used within your company.

Let’s suppose that someone in your company sends an email campaign that contains broken links. These messages generate a lot of spam complaints and your ISP flags your top level domain. Now all emails sent from your company domain will be affected. This is a huge problem that could have been controlled by using subdomains.

With that said, using subdomains can affect the main registered domain's reputation. But the advantage is that subdomains can only affect each other indirectly.

For example, let's say that you send messages using the subdomains notify.example.com and newsletter.example.com. If you make a mistake with your newsletter and ruin the reputation of newsletter.example.com, you can expect to see some kind of dip in the reputation for example.com as well.

By sending transactional mail over notify.example.com, however, it won't suffer a reputation hit at the same rate. It's only able to be affected indirectly by the smaller reputation hit to the main registered domain.

Because they affect each other indirectly, this means that in many cases subdomains can have wildly varying reputations, which is often vital for protecting your most important mail streams.

4 tools to help you monitor domain reputation #

If someone wants to assess their reputation, they can ask credible sources around them. Similarly, to understand your domain reputation, you have to go to reliable sources. Here are a few tools you can use to find your IP reputation. 

1. Google Postmaster Tools #

Postmaster tools help organizations understand why their emails were sent to spam.

Google Postmaster tools homepage
Google Postmaster Tools

Gmail’s reputation scores are broken out by both domain and IP address. The following tabs are available in the Google Postmaster Tools dashboard:

  • Spam Rate – What percentage of your DKIM-authenticated mail caused Gmail users to complain.
  • Domain and IP Reputation – What Google thinks of your domain(s) and the IP(s) from which they’ve seen your authenticated mail.
  • Authentication – How much traffic using your authentication domain(s) has passed authentication checks – SPF, DKIM, and/or DMARC, as applicable.
  • Encryption – How much of your mail was sent using TLS encryption between the sending server and Google’s servers.
  • Delivery Errors – Various metrics showing errors that your authenticated mail may have experienced.

Reputation levels

Gmail’s reputation scores are broken out by both domain and IP address. It assigns a reputation score of Bad, Low, Medium, or High. 

  • Bad — A history of sending an enormously high volume of spam. Mail coming from this entity will almost always be rejected at SMTP or marked as spam.
  • Low - Known to send a considerable volume of spam regularly, and mail from this sender will likely be marked as spam.
  • Medium/Fair — Known to send good mail, but is prone to sending a low volume of spam intermittently. Most of the email from this entity will have a fair deliverability rate, except when there is a notable increase in spam levels.
  • High — Has a good track record of a very low spam rate, and complies with Gmail's sender guidelines. Mail will rarely be marked by the spam filter.

2. Senderscore.org #

Senderscore is a service that measures your domain reputation and offers suggestions on how to improve it. It is derived from a proprietary Return Path algorithm, and represents an IP address’s overall performance against metrics important to both ISPs and their customers who receive your email.

Senderscore homepage
Use Senderscore to learn your reputation

You can pull Sender Score metrics for your domain that’ll include details such as:

  • MX Record
  • SPF Record
  • SSL Certificate
  • Domain owner
  • Issue date
  • Expiration date of domain
Senderscore metrics
Senderscore Metrics

3. Talos Intelligence #

Another reputation service that provides a score of Good, Neutral, or Poor. Talos Intelligence (by Cisco) provides additional data on email volume and volume history.

Talos Intelligence homepage
Use Talos Intelligence to assess your reputation
Talos Intelligence metrics
Talos Intelligence data results for the specified domain

You can search by IP, domain, or network owner for real time data. In this example, we’re searching for data specific to the example.com. The Reputation Details section includes data about the content your host on your website, which may be of higher or lower reputation in relation to your email.

The best email indicators will be at the bottom under Additional Information

Senderbase detailed metrics breakdown
Additional information shows the top addresses used to send emails for your domain

The Email Reputation column refers to IPs sending on behalf of the domain. This will let you know if there have been any issues. Keep in mind, Talos may not show any data if you don’t send enough volume.

4. MXtoolbox #

If your domain reputation is low and you’ve had it for some time, you may want to find out if its been blacklisted by any ISPs. MXtoolbox is a great reference for these scenarios. They have a domain health check that executes hundreds of performance tests to make sure all of your systems are online and performing optimally. The report will then return results for your domain and highlight critical problem areas for your domain that need to be resolved.

MXToolbox domain health metrics
MXtoolbox Domain Health report

Postmark and domain reputation #

If you’re sending through Postmark (or are thinking about it), we take care of the infrastructure for you by keeping our IPs clean, throttling our sending rate to ISPs, and properly managing bounce and spam complaints.

We also encourage customers to set up DKIM and a custom return-path to be complaint with DMARC, not only to improve deliverability but also to improve domain reputation. Our DMARC weekly digest is a free tool you can use to monitor and implement DMARC. We process reports from major ISPs about your domain's DMARC alignment and send these details to you every Monday, for free.

Postmark DMARC sign up
Sign up for Postmark DMARC weekly digest to monitor your domains

High-reputation IPs #

Postmark can also help improve your domain reputation because all of our IPs maintain a high reputation. This can affect your domain reputation in a positive way: Postmark customers generally see much better deliverability on our shared pool than on a dedicated IP. 

That’s because a high-quality shared pool means mistakes you might make are padded from affecting deliverability. While a dedicated IP is extremely sensitive to errors in sending or in your list, it can only have a reputation as good as your own sending practices alone. 


Monitoring your domain health isn’t just a one time ordeal. It’s an ongoing process that requires consistent nurturing. 

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This post was originally published Jun 21, 2018

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