Email Sender Reputation Fundamentals

IP/domain reputation is a score assigned to an email sender by an Internet Service Provider (ISP). It affects your email marketing campaigns, inboxing, and email performance. The higher the score, the higher the chances of emails landing in inboxes. You can gather insights to monitor the reputation from multiple sources, as the scoring system varies depending on the ISP.

Before learning about the sources for reputation insights, it is essential to understand the following factors that influence the sender reputation:

• List Quality
• Email Marketing Practices
• Email Content
• Monitoring Sender Reputation

List Quality

List quality is of the utmost importance when it comes to the sender reputation. Your list of email addresses decides the fate of your email marketing for the most part. That’s why you need to pick your email subscribers’ sources carefully.

You can use various sources to have a good-quality list of email subscribers:

• Email opt-in: Use the opt-in information of the users who subscribe through your website signup or contact form via the double opt-in method (Single opt-in is also acceptable)
• Validation: Validate subscribers through double opt-in and captcha
• Email validation tools: Validate users that you have collected via calls, direct/offline marketing, physical forms, etc., using email validation tools (e.g., Validation, Validity, Zero bounce, Neverbounce, etc.). Otherwise, you might miss the invalid emails, negatively affecting your reputation.

You may consider following the bad list acquisition actions below to avoid unhealthy subscriber lists:

• Do not send emails to an old email list that has not been used for more than 6 months to 1 year. This list needs cleaning and introducing into your email marketing program in small chunks. Based on the performance, you can gradually increase the volumes you use from this list. An old and inactive list might have a negative impact on your email marketing performance.
• Do not rent/buy subscriber lists. These users never subscribed to your marketing campaigns, may have disabled email boxes, or may not even exist. Such lists might result in high bounces, spam complaints, and spam trap hits.
• Do not let your bounce rate be higher than 2%, as such lists might imply that your list acquisition methods are faulty.

Email Marketing Practices

Sending practices play an important role in your sender reputation. You can refer to the following best practices to maintain a healthier email marketing strategy.

• Proper warm-up: If you are sending messages from a new IP/domain, it is most likely that your sending servers have no reputation. The ISPs and spam filter algorithms are more aggressive and active when it comes to anything new in email. That's why you need to follow a proper warm-up plan based on your list size. You can start with low volumes and increase them gradually. This will let your recipient servers/ISPs analyze your sending behavior and adjust your reputation accordingly. 
• IP/domain black lists: You should monitor your IP/domains for black lists. Various black listing organizations monitor the email flow (e.g., third parties such as Spamhaus, Barracuda, etc., ISP-based organizations such as Hotmail, Office365, Cloudmark, etc.). You can get support from your deliverability experts to take any necessary actions. You should avoid high volumes until such issues are resolved.
• Volume spikes: You should not increase your volumes by more than 25% at once after you reach the peak. A sudden rise in your sending practice might trigger the spam filters. You can get support from your deliverability experts to gradually increase volumes to a desired level.
• Spam complaints: Spam complaints significantly impact your sender reputation. You should keep your spam complaint rates below 0.1% for each ISP. If your users are frequently reporting spam complaints and more than 0.1% of your subscribers do not want to receive emails from your brand, you might consider changing your list acquisition methods and seeking more relevance in your email content. 
• User engagement: Your email campaigns should have consistent open rates and click-through rates, which will give you insights into user engagement. 

Email Content

Your email content determines the user response, which in turn determines the sender's reputation. Content is the key to an email marketing sending reputation. After whom you target in your email campaigns, what you share in these email campaigns is the second most important factor.

• Your content should always be relevant to what your email users subscribe to.
• You should personalize your emails as much as possible.
• You should have clear CTAs.
• Your email has an easily reachable objective.
• You should not confuse your users with multiple action points.
• Your subject lines or email creatives should not be too long. For example, subject lines should not exceed 30-40 characters.
• You should provide easy opt-out or unsubscribe options in your campaigns.

Monitoring Sender Reputation

Some ISPs (e.g., Google, Hotmail, etc.) provide free postmaster services and email sender reputation insights as follows:

Google Postmaster IP/Domain Reputation

Google assigns the reputation on a scale of HIGH-MEDIUM-LOW-BAD and GREEN-YELLOW-ORANGE-RED, respectively. The spam rate and delivery error rate should be flat at 0% or about 0.1% and should not exceed this.

Smart Network Data Services (SNDS)

SNDS is a postmaster service provided by Microsoft for all of its affiliates. 

These are the aggregate results of the spam filtering applied to all messages sent by the IP during a given activity period.  The table below displays the colors that represent a spam verdict on a message. 

You can use platforms such as SenderScore, Barracuda Central, etc. to check your sending reputation, and other platforms such as Multirbl, Mxtoolbox, etc. to see your IP/domain black list details.