I'm posting here first (rather than submitting a bug report on GitLab) because I'm not sure if I've overlooked a configuration setting.
We're running the latest versions of the various Mailman 3 packages on Ubuntu 20.04, using Postfix as the MTA.
Mailman 3 has been configured to apply DMARC mitigation unconditionally, replacing From: with the list address.
The situation we're seeing is that if person A sends an email from a Google account to Mailman 3 and receives the (modified) post back from Mailman 3, the message ID is not being changed. Google's behaviour then is not to show that message to the user because it thinks it is the same message that the user sent out.
Since Mailman 3 is modifying the message, it ought to have a different message ID.
Is that a configuration setting I've missed or a bug, please?
Thank you.
Regards
Philip