How to add custom mail headers and List-Unsubscribe to a mail merge

If you want to change mail flow based on a custom header in your mail merge or add a List-Unsubscribe header to your mail merge, our guide will show you how.

Open advanced options

Toggle advanced options

In the campaign manager select the link titled "Show advanced campaign features" to open the advanced options.

Option: Custom Header Name and Value

If you want to add a custom header to the email in order to process messages sent through SecureMailMerge in your Exchange mail flow settings, you can specify the header here.

Note that custom headers must start with x- (e.g. x-sent-by or x-mycustomheader).

Option: List-Unsubscribe Header

If you wish to add a List-Unsubscribe header you can specify the value here.

Unless you are using a third-party service for subscription management it is recommended to set the value to (including the angle brackets):

<mailto:[email protected]?subject=unsubscribe>
and replace the [email protected] with your email address.

This will fulfill the new requirements by some email providers to require a one-click List-Unsubscribe header from February 2024 but not that these rules only apply if you send more than 5000 emails per day. (Currently setting the 'List-Unsubscribe-Post' Header is not supported in SecureMailMerge.)

Dynamic values for the header values

Instead of using the same value for all recipients, you can also read this value from a spreadsheet field. For this simply enter the name of the field in curly brackets. For example if you have a column named "HeaderValue1" in your spreadsheet, you can enter

as the value.

This applies both to the custom header value field and the List-Unsubscribe value.


In order to see the header fields in Outlook (either in your test message or Sent Items) you need to open the message, click on "File" in the menu (if you don't see it, open the message in a separate window) and then select the "Message Options" tab. There you will see the headers in a plain text format.