1. What is Sender Reputation?
Sender reputation is how ISPs evaluate the credibility of email senders, based on two main factors: the sending IP address and the sending domain name. This is information about the origin of the email. The relationship between reputation and email delivery performance is clear: the better the sender’s reputation, the more trust the ISP has, and the higher the likelihood of the email reaching the recipient’s inbox.
It’s not as simple as getting a score like “your sender reputation is 94%”. Instead, it’s more of a relative scale: high, medium, or low reputation.
2. Factors Affecting Sender Reputation
IP address is the most important factor in sender reputation. There are two types of IP:
Private IP:
- Under the complete control of the sender
- Takes time to build reputation with ISP
- Cannot send large volumes of emails from a new IP immediately
Shared IP:
- Shared with other senders
- Influenced by the sending behavior of shared users
- Usually provided by ESP (Email Service Provider)
Domain reputation also plays an important role:
- ISPs evaluate both primary and secondary domains
- Check the domain names of images and links in emails
- Influenced by interactive factors
Other factors that affect reputation:
- Emails entering spam traps
- Sending frequency and consistency
- Bounce rate (hard bounce and soft bounce)
- Number of emails sent to unknown addresses
ISPs will lower their reputation if they detect many invalid email addresses in their sending list.
3. Sender Reputation Best Practices
You should look at the sender score for your IP addresses. Aim for a score of 90 or higher, as the higher the score, the better your inbox rate.
If you have the budget, you can sign up for a WarmUpInbox service to improve your sender score and deliverability. Look at your performance metrics to determine whether this is financially viable, especially if your deliverability is significantly improved.
4. Segmentation and Email Management
Segmentation helps track issues in email campaigns. It can be segmented by recipient engagement, email content, or email type (transactional/marketing). Segmenting transactional and marketing emails to different IPs helps control the reputation of each type. However, avoid spreading too many IPs as this is a common spammer tactic (snowshoeing).
There are two types of bounces: soft bounce (temporary rejection due to server down/full mailbox) and hard bounce (email does not exist). Soft bounces can be re-attempted, but should be deleted if they fail for a month. Hard bounces should be removed from the list immediately.
List hygiene is the process of cleaning up invalid email addresses. It should be done regularly, at least once a year. Unclean lists lead to low open rates, high bounces, and ISPs may move emails to spam or block them completely.
5. Bounce
Soft bounce is when an email is temporarily rejected due to factors such as a server down or a full mailbox. You can resend it later, but consider removing it if the email continues to soft bounce for a month.
In some cases, soft bounces are due to policy issues such as blacklisted IPs or connection errors. In these cases, the problem should be fixed instead of removing the recipient. Monitoring the bounce log will help determine the exact cause.
Hard bounces occur when an email is sent to a non-existent or closed address. These addresses should be removed from the list immediately. Each email management software has its own way of handling bounces, so find out the options that are appropriate for your system.
6. Email List Hygiene
Email list hygiene is like brushing your teeth – a process that needs to be done regularly to maintain cleanliness. Email addresses can become inactive when users abandon them.
Unclean lists lead to low open rates and high bounce rates, which lower your sender score. Clean your list at least once a year, or use Mail Floss to automate daily cleaning.
When ISPs detect low open rates and high bounce rates, they will move emails to spam or block them altogether. This is an important step that should not be skipped to maintain effective email marketing.
7. Blacklist Monitoring
Periodically check the blacklist database to see if your IP or domain is listed.