On 4 Apr 2025, at 9:41, Alessandro Vesely wrote: > 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.
They don’t always do that. A “transparent forwarder” (think ~/.forward or /etc/aliases in *nix) typically leaves the envelope-from address alone. That is a long-standing behavior that isn’t likely to change. > 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. But that wasn’t the point of my comment. I’m not the operator of a large mail domain—so correct me if I’m wrong—but don’t some large domains have separate infrastructure for incoming and outgoing mail? It isn’t a matter of just sending the message back to the the MTA that sent it, because it may not be set up to receive mail from outside at all. As I said, large domains probably have ways to solve the problem of associating the bounce with the bounced message. But I’m wondering if that is a problem that needs to be acknowledged. -Jim _______________________________________________ Ietf-dkim mailing list -- ietf-dkim@ietf.org To unsubscribe send an email to ietf-dkim-le...@ietf.org
