How to Avoid Ruining Your Domain Sender Score

How to Avoid Ruining Your Domain Sender Score

April 25, 2017

Email is one of the most effective marketing communication channels. $1 invested in email returns an average of $38 in revenue. For sales teams, the importance is even more explicit. A single, well-crafted email can mean thousands of dollars in potential revenue from a single customer.

Therefore it is critical that this channel to your customers and potential customers remains open. A low domain sender score will ruin your email reputation and quickly close that door. Your domain sender score is your trustworthiness score for mailbox providers. It's what decides whether they let you deliver your emails to their users, or whether they think you are spam and send your message into the ether.

Not understanding your sender score and what goes into it will reduce your ability to reach leads and customers, and more importantly directly hurt revenue. Understanding your sender score and how you can increase your score and deliverability of your emails, helps you make sure you can always reach the right customers without fear of being blacklisted.

What is your sender score?

Your sender score is a proxy for your domain's reputation as an email sender. The most natural analogy is with your credit score (credit history). The higher it is, the more mailbox providers—Gmail, Microsoft, Yahoo, et al.—are going to trust you with access to their customers. When it's low, you can find your emails undelivered or your domain blacklisted and unable to deliver to that mailbox at all.

There are a number of different companies that assess your domain sender score:

For some of these scores, you can checkout your domain or IP right now to see your current score. Whichever you choose to follow, they will take into consideration the following information to compute your score:

  • Complaints: How often your emails are “marked as spam,” or forwarded to a postmaster or blacklisting service to make sure they are removed from the recipient's inbox?
  • Blacklists: Is your IP address or domain already on a blacklist for previous email abuses?
  • Sending to spam traps & unknown users: Are you consistently sending to email addresses that are out of use or set up to catch spam lists?
  • Engagement: Does your content have low open rates, reply rates, or other metrics of engagement?
  • Consistent volume: Are you sending to the same-size list constantly? You can be penalized for sending to fluctuating size lists as it shows that you don't have a consistent user base.
  • Consistent frequency: Are you sending on a regular basis to that list. Again, changing the frequency constantly can hurt your score.

How each of these are weighted is different for each proprietary algorithm. But the most important offenses are sending to people who complain and sending to non-existent addresses. These are red-flags for spam.

The importance of sender scores for sales & marketing

It is vital to continually check and improve your sender score for two reasons.

  1. If you have a low score, then your email will not be reaching the people you expect. They'll be undelivered or spammed. You'll have low engagement. You'll make less $$.
  2. Your sender score is a symptom, not a cause of bad email etiquette. If your score is low, that means you aren't sending high-quality content to high-quality addresses.

Effectively, your sender score is not just a proxy for your reputation with mailbox providers. It is also a proxy for your reputation with leads, customers, and prospects. A low score means that you are not only not reaching the right people, but that you are not respecting the people you are reaching. It also gives you a measure of your efficiency.

This might seem that you are beholden to your recipients and random companies for whether your marketing emails or prospecting emails will be a success. But just like your credit score, your sender score is under your control.

The good news is that your sender score is dynamic. Return Path's Sender Score, for instance, is calculated on a 30-day rolling average. This means that if your score is currently low it can be improved and you can go from 0 to 100, or from poor, through neutral, to a good rating.

If you have a good sender score (for instance, above 80 on Sender Score) then you should look for continual ways to optimize your marketing and keep your score high. If you have a sender score less than 80, it can be rescued. Each of the data points used by companies can be improved through good list practices and good email practices.

How to avoid ruining your domain score: quality and hygiene

This entire process is in your control. Just like with credit scores, following a few basic guidelines can get you to a top score.

The quality of your email list is perhaps the single most important determinant of your sender score.

If you email a list that contains a high number of non-existent or non-working addresses, this is a strong signal to mailbox providers that you aren't taking time and consideration in your email marketing. They won't want to risk you sending ill-targeted emails to their customers, so they will blacklist you for this.

Therefore, having a list with a low bounce probability sets you up for success. Having a high-quality list comes down to two things:

  1. List Quality: Getting correct email addresses in the first place
  2. List Hygiene: Constantly assessing and pruning your list to only email desired recipients

List quality

The first hurdle is high-quality email addresses. If you are using a lead generation form, it's possible people will use a fake email address just to get access to gated content. You should verify these addresses either through a double opt-in verification email or through enrichment (

If you are building an outbound list, then you have to be extremely careful about using the emails on the list. Suppliers that emphasize quantity over quality will include unknown user and spam trap addresses that will kill your domain reputation:

  • Unknown users: An unknown user could be an email that never existed in the first place, or has been abandoned or terminated. These will return a 550 error code. If just 1 in 10 of your emails returns a 550 error, this will cause email deliverability issues for the rest of your list. If you then resend to those addresses and it bounces again, it signals to mailbox providers that a) you don't care about list quality, and b) you don't care about list hygiene.
  • Spam traps: These are email addresses set up exclusively to catch spam marketers and list providers that indiscriminately scrape websites for email addresses. The email address is usually hidden from human view but will be harvestable for a bot. If you send an email to a spam trap, it shows you aren't actively trying to reach real people and your domain reputation will take a severe hit.
  • Email guessing: Some email list providers will include calculated (or guessed) email addresses that are typically some combination of first name + last name Lists of generated emails typically have an average bounce rate of 30% and will quickly destroy your sender score.

List hygiene

If you are unsure of the legitimacy of the emails on your list, then enacting list hygiene techniques can ameliorate this to a certain extent:

  • Remove obvious email addresses that have no specific end-user (,, as well as common errors (
  • Quarantine new information and check for these errors before adding to your main email list.
  • Email regularly and consistently so that bad addresses are removed over time.
  • Use bounce management to determine the source of bad emails.

This last technique, bounce management, is something that you should take seriously. It allows you to make sure your list gets more accurate over time, increasing your domain score. As each bad email is sent back, don't just delete it from your list. Use the data gathered to find out where you got this specific email from and why it bounced. If it was from a user, look at double opt-in and other verification options. If from a list, use a different provider that emphasizes quality over quantity.

Continual improvement

Though list quality is the most fundamental component to a high sender score, your score is a combination of other factors that you should also take into account:

  • Email content: Anti-spam filters will scan your emails looking for red-flag content and issues. While some words that will get you blacklisted are well-known, other elements that evoke filtering are high use of images, and incorrect use of HTML. Check that you have a good balance of text to images in your email, and that everything is rendered correctly.
  • Engagement: Marketers will use engagement metrics to assess the success of their campaigns—opens, clicks, conversions—but mailbox providers will also look at these metrics to determine the quality of your emails. Low engagement is a signal that the content is unwanted and therefore spam. They also have access to extra quantitative information about your campaigns such as spam complaints, forwarded email, and email archive rates, that they can use to effectively monitor your comprehensive reputation.
  • Consistency: You want to send to a regular list on a regular basis, showing that you are just flooding the mailbox providers' customers with email spam. You want your list to grow naturally over time instead of adding masses of new emails all at once.

Each of these points are important whether your list is inbound or outbound. Ultimately what separates legitimate email marketing and sales from spam is targeted content to a targeted list. Curate a great list, send some great emails, and you'll always have a solid sender reputation and stay out of your prospects spam folders.

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