https://serverfault.com/a/674984/255397 deals with the rewriting of the sender address (envelope and header) for E-Mails which are sent out to another system.
I don't understand, why smtp_header_checks is necessary, additionally to sender_canonical_maps. The answer states that this would be needed for smtp relayed mail.
However, the documentation says, that the scope for Canonical address mapping is "all mail" (see table). So for me, it looks like smtp_header_checks is unnecessary. What am I missing?
