On 2022-10-05, Steve Fairhead <st...@fivetrees.com> wrote: > I have several OpenBSD email servers, some elderly (Sendmail) and some > brand-spanking new (smtpd). Recently I've noticed that some (of both > kinds) are failing to deliver mail to some major UK ISPs. (Mostly > domestic; business ISPs not so much.) > > For Sendmail, the error is "TLS handshake failed"; for smtpd, it's > "Network error on destination MXs".
Can you show some example servers that are having the problem? Has anything changed network-wise on your side that might coincide with this breaking? > I do have SPF etc setup; thought that might be it, but no. I've read > that some ISPs have closed port 25. I presume that's relevant, but I > simply don't know. Delivery to MXes is done on port 25 so nobody is closing that on the server side. Some access ISPs may filter port 25 (and if so, may or may not have a way to unblock it) but that would usually block everything on port 25, not leave some working. Shot in the dark: you could try lowering MTU as a test. -- Please keep replies on the mailing list.
