Upcoming changes to how we identify bounces/fbl/ebm


Staff member

Starting with MailWizz 2.1.0 we are changing the way we identify bounce emails, feedback loop emails and email box monitor emails.

Until this version, we used to inject headers like {PREFIX}-Campaign-Uid / {PREFIX}-Subscriber-Uid in the campaign emails so that later we can use these headers to identify the subscriber and the campaign so we know against whom we take actions.
Historically, we needed this because we did not have any other way to identify an email that returned. However, a few years ago, because of some changes to delivery servers, we had to start registering each message id of each email that goes out for campaigns.
This means, that for years we have had an alternative way to identify emails, and we should not rely on custom headers, rather we can use a standard header, the Message-Id header.

Why this change you might ask.
The reason is, some emails that MailWizz has to process, will not contain these custom headers, for various reasons, and in this case, we cannot process those emails and we're missing bounce/fbl/ebm emails. So this is us taking an extra step into making sure we can actually better process these emails.

This also will make the size of the emails a bit smaller, as we have removed many of our custom headers, so in turn will make delivery a bit faster and bandwidth usage a bit smaller, all in all, a win.

With this change, 3rd-party tools ( like this one ) will have a harder time identifying the message since they don't know the campaign and subscriber ids.
In order to fix this problem, we will add a new API endpoint so that you can get a delivery log based on a given message id.
This delivery log will contain the campaign info, list info and subscriber info for the given email.

The 2.1.0 version is planned to be released in January 2022, so if you have questions related to this, please let us know.
MailWizz 1.x will continue working like it is, no changes will be made there.

Thank you.