This is incorrect. The return-path is the address used by receiving the MTA to send bounce messages to when the recipient's 5322.From is unreachable for whatever reason.
So if your MLM sends a message to a non-existent address or there are some other delivery errors post-acceptance, then a bounce message will likely be sent to your 5321.from address, not the 5322.From. Many mailbox providers do not reject during the SMTP conversation, but accept the message and generate a bounce later in their MTA chain. So it is important to monitor your 5321.from at all times. This is true of all internet mail, not just MLM traffic. Ken. ________________________________ From: Axel Rau <axel....@chaos1.de> Sent: Wednesday, 15 June 2022, 19:18 To: Ken O'Driscoll <k...@wemonitoremail.com> Cc: mailop@mailop.org <mailop@mailop.org> Subject: Re: [mailop] Best practice for mailing list servers Am 15.06.2022 um 19:43 schrieb Ken O'Driscoll <k...@wemonitoremail.com<mailto:k...@wemonitoremail.com>>: If your return-path is a CNAME, then you'll have problems with bounce processing too. Many MTAs will consider the return-path invalid when they can't find an MX RR; as will many message filters. Their behaviour is wrong. As we all know, MX is only needed if I send mail to a domain. The MLM is a host and needs no MX. Return-path domains really need an MX record for mail to work properly. Why? Axel --- PGP-Key: CDE74120 ☀ computing @ chaos claudius
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