On Wed 02/Apr/2025 23:48:23 +0200 Jim Fenton wrote:
Section 2.3: I’m wondering how sending bounces in reverse along the same path will work for large domains. Presumably it does an MX lookup of the sending domain? There might be incoming third-party mail handlers, and the domain itself may have a lot of mail infrastructure. It seems like a non-trivial problem for a large domain to associate the bounce with the message it came from. But I suppose a large domain has the resources to solve that problem.
My understanding is that it means forwarders /always/ rewrite the bounce address. It could be SRS or anything to a similar effect.
Keeping the original bounce address, alias forwarding in the SMTP spec, has a lot of shortcomings. In the event that the alias target suffers a mailbox full error, the message bounces to someone who can do nothing about it. Worse, if the forwarder does not check the bounce address, it becomes similar to an open relay, where anyone can send malicious material to anyone else in the form of bounces. It is wise to replace bounce addresses.
It is less wise, IMHO, to try and remove trace fields added by downstream servers, unless there are cogent privacy issues.
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