Management and operation of the Suppression list

When working with mailing lists or our company's contact databases, we may encounter situations where some of our messages don't reach their intended recipient (despite a clear opt-in from our contact). Such email addresses are placed on a suppression list thanks to Microsoft's automated system. In this article, we'll focus on understanding the general principles of how such a list works and how to manage it, for example, to fix problems that caused an email bounce.

What exactly is the Suppression list?

This built-in, non-deactivable backend tool aims to maintain a company’s reputation by filtering emails that could negatively impact its reputation.

Like any tool, especially an automated one, without the knowledge necessary to use it correctly, it can cause more harm (e.g., time) than benefit. So let’s focus on what type of email address can be included on the Suppression List.

Emails damaging to the company's reputation

• A hard bounce is an invalid email address, e.g., with a typo or deleted by the user (sending such emails increases our spam rate, and sending such messages too often could block the sender – the company – by the email provider, e.g., Gmail).
• Addresses that mark our email as spam (feedback loop/spam report) – these addresses mostly apply to situations where our email reaches people who did not want to receive messages from us or did not subscribe to our mailing list at all.
• A soft bounce is a situation where the address is correct, but there is a temporary failure, e.g., a server problem, too-long request time, an overflowing destination mailbox, or failed email authentication. After five such bounces in a row, the email address will be added to the skip list.

How is the Suppression list organized?

Hard bounce collects addresses at the organizational level and stores them for 180 days, as in rare cases a hard bounce may become a working address again.

Similarly, at the organizational level, the Exclusion List contains addresses that have marked our email as spam. However, these do not expire automatically.

A special type of category: manually set patterns – are managed by deliverability engineers. They contain domains and email addresses that are not good targets for email campaigns – these are test email accounts or temporary domains.

We can configure the segment and treat it as a suppression segment – although technically it is not a suppression list, it can be a useful tool, especially since we have full control over it.

Appearing on the Ignore List is not usually permanent. Depending on the number of occurrences, the system assigns a different blocking time to a given email if it is a soft bounce (listed) or a hard bounce originating from a domain belonging to the organization sending the email. In such cases, these are respectively:

Manual management of the Suppression list

Although the tool itself is automatic and will “release” the email address from the Ignore List after a specified period of time, it is possible to do this manually, e.g., when the problem has been resolved.

To get started, go to the acquisition process (journey), which includes rejections:

Next, in the panel on the right, select the delivery funnel and click the blue preview icon:

We select „blocked” and find the entry we are interested in.

Finally, click on the profile name, which will take you to Contacts and the record you are interested in. Go to the Communication tab. At the top of the screen, you should see a message if the contact is on the Ignore List:

Select the Manage button on the right side of the message and in the new window decide whether to remove it from the list or not:

Although the documentation states that emails on the Ignore List due to “invalid-mailbox” cannot be removed from it, the practice shown in the attached screenshot indicates otherwise.

If an email address is saved with an error, simply correct it in your profile – you do not need to delete it manually from the list.

Restrictions on managing the Suppression list and support department

According to official documentation, there is a limited number of attempts to remove email addresses from the Ignore List. Once this number is exceeded, it is recommended to contact support, e.g., when the number exceeds several hundred. It is assumed that this is unnatural behavior and that something must be wrong with the system. Since this number is not specified, it is possible that such a limit does not actually exist. Nevertheless, it is recommended to contact support in case of hundreds of results.

If we decide to take this step, the following materials should be collected:

• A list of email addresses to which the request applies (please note that this is case sensitive, so pay attention to upper and lower case letters)
• Reasons why we believe that each of the addresses on the list should not be included in the Suppression list
• Proof that each of the addresses is active and can receive emails from other email providers, e.g., by providing a screenshot of such an email or a copy of an email received from the email address in question
• What steps will we take to prevent this from happening again (if applicable to the current situation)

Summary

The automatic exclusion list will protect our company’s reputation from restrictions imposed by email service providers, but it requires us to be familiar with the mechanisms discussed so as not to generate unnecessary chaos in the mailing process.

Taking care of your contact database and regularly checking the entries on your list can help you improve the quality of your database. If we cannot afford to wait 7, 14, 30, or 180 days (depending on how many times a given email has been added to the Ignore List) or if we have solved the problem earlier, we can manually remove the email address from the list.

Sources:

• Microsoft Learn: Suppression lists
• Microsoft Learn: Email bounce categories