Sender reputation guide

Keeping your reputation is the most important part of sending emails. As a sender, you want to gain high performance and inbox placement. Sender reputation is how ISPs measure the trustworthiness of a senders IP or domain, by analyzing a variety of metrics. ISPs use sender reputation to determine whether an email should be accepted via inbox and spam filter placement.

This topic describes how to achieve and keep up a good sender reputation. Before moving on, it is of help to understand the basics of email and spam filtering.

Email filtering and spam filter systems

Email filtering is a technique to filter a server's inbound and outbound email traffic. This technique is used by ISPs and organizations such as your internal IT department to filter and scan messages sent to their recipients. The spam filter systems have a various amount of classifications for incoming mail. Some include virus, adult content or spam, among others.

Most spam filter systems have the ability to perform the following:

• Allow or decline incoming mails based on history of IP sending analysis, engagement activity and Realtime Blocklist listings.
• Allow or decline emails coming from IPs that have/have not been allowed. The majority of ISPs no longer support IP allowlisting.
• Antivirus support to prevent mailings from entering the recipient’s inbox that have malicious code/attachments.
• Allow or decline emails based on content analysis. These systems use their own internal algorithms to block mailings based on words used, attachments sent or HTML syntax concerns to name a few. For more information on how to avoid content flaws, see Email content best practices.

Developing a sender reputation

Reputation is primarily based on your businesses sending behavior, and how your recipients engage with your email. Think of it like having a credit: if you do not follow the best practices, for example paying on time and keeping low debts, this will negatively impact your credit score, leaving you unable to gain certain financial benefits. In the same way, ISPs will rate you based on your sending behavior.

Email service providers and email filtering systems work together to monitor sending of unwanted email in order to reduce email spam.

Your data is an important part of your reputation and the way you attained your marketing list is one of the main factors that can affect your sending reputation. If you are sending to a list with inactive email addresses (for example closed email accounts, typo addresses, spam traps) you will experience future reputation issues.

It is essential to always send a double opt-in confirmation email before sending to a list, where there is a high possibility of inactive addresses. Marketers with a good data list will see good sender reputation and inbox placement, and those with poor reputation will often see emails entering the spam folder or blocked entirely.

Factors that affect your sender reputation

• High abuse complaints
• Recipient engagement, opens, click-through rates performance
• Recipient list quality, including spam traps and unknown users
• Infrastructure and authentication (SPF, DKIM, DMARC)
• Content
• High unsubscribe rates
• Sending history
• Engagement
• IP permanence
• Inconsistencies in the volume of emails sent
• Number of recipients that mark your emails as spam
• Times you have hit spam traps
• Blocklisting of your IP/Domain
• Number of bounces you receive
• ISPs track engagement, low opens, reply to emails, forwards, as well as high deletes and unsubscribes

Tips for achieving good sender reputation

ISPs' main goal is to protect their users from malicious content and to accept only emails that a recipient really wants to read and engage in.

Follow these tips to achieve a good sender reputation:

• Send a welcome email to start off, a series of emails to gather an insight into your recipient’s engagement behavior.
• As months pass, keep an eye on recipients who have not opened your emails yet, occasionally removing them from your recipient list.
• Ensure you are targeting your users based on information and content they would like to receive, using targeting and marketing segmentation techniques.
• Review your list hygiene process, implement form verification tools such as CAPTCHA and form validation through API. Ensure your data has been attained through a permission-based process such as DOI and stay away from third party or bought lists.
• If a recipient keeps receiving an email each day from the same sender, they will end up unsubscribing, or making a complaint. Consistency is important, review the frequency of your emails, limiting recipients from receiving no more than 1-2 emails per week.
• Send emails based on recipient engagement: Low engagement impacts your reputation. Ensure you are sending to recipients with high opens and click rates.

Maintaining your reputation means continuously taking a proactive step to follow best practices. If in doubt of a marketing list, avoid to send to that data. The result from a bad send could either have a negative effect on your delivery immediately or later down the line.