Use case: Incoming mail should be copied into a discourse topic through bcc. DIscourse receives this mail from the mailserver through pop3.
The mailserver has a recipient_bcc_maps table (see http://www.postfix.org/postconf.5.html#recipient_bcc_maps) which adds a bcc header with a discourse+extension target address.
But the incoming mail is rejected by current Discourse 3.5.0.beta1-dev with error msg
Email::Receiver::BadDestinationAddress](https://forum.netzwissen.de/admin/email/rejected)
It looks as if Discourse only reads the to and/or cc. fields, but not bcc. Therefore it does not detect the correct discourse+extension address.
See also old topic Email with correct incoming email address in bcc is being rejected