On Mon, 30 Sep 2024, Quelrond wrote:
It seems that OpenSMTPD sends non-delivery reports with blank 'From' field. Our ISP relay does not like it. Is there any way to put a 'correct' smtp address to use for NDR sending?
Empty MAIL FROM is the only correct way to send NDR. If the sender doesn't like NDRs (or are just broken), then just drop the NDR. On sendmail, I had a per sender policy using SRS to send the NDR disquised as a reply with a special localpart to prevent loops. The RFC defines empty MAIL FROM as equivalent to postmas...@example.com. The empty MAIL FROM prevents an NDR to an NDR. The postmaster mailbox MUST be deliverable, so if you absolutely have to accomodate broken senders for business purposes, use a special mailbox like n...@example.com that refuses all attempts at delivery at MAIL TO (envelope stage).
