Thanks everyone for your insights! @Bernardo: I wasn´t aware that a delayed greeting could happen in the order of 20 seconds or so. That did the trick!
@Wietse: Thank you as well for showing me how the transport maps work! Case closed. Regards, Sebastiaan On Saturday, July 23, 2022 18:36 CEST, Bernardo Reino <rei...@bbmk.org> wrote: On Sat, 23 Jul 2022, Sebastiaan la Fleur wrote: > > Hello everyone! > > Currently I am running into an issue that a (misconfigured) destination > mailserver does not accept mail on port 25. It allows a TCP connection but it > will not send a greeting. Instead, it expects mail to be send to port 587 > which seems to accept both mail with and without starttls. > > Looking into the logging of my postfix instance, I can see that it tries to > connect to port 25 but the destination mailserver will never reply with a > "initial server greeting": > > [ stripped excessively verbose log ] > > Jul 23 15:39:20 smtp postfix/smtp[382]: 9ECFB7800D3: > to=<willnotw...@kuiperschuttingen.nl>, > relay=mail.kuiperschuttingen.nl[185.104.29.14]:25, delay=314, > delays=299/0.03/15/0, dsn=4.4.2, status=deferred (conversation with > mail.kuiperschuttingen.nl[185.104.29.14] timed out while receiving the initial > server greeting) Maybe you have reduced some timeout? I can telnet to the MX host, port 25, and I get a greeting (after 20 seconds or so). $ telnet mail.kuiperschuttingen.nl 25 Trying 185.104.29.14... Connected to mail.kuiperschuttingen.nl. Escape character is '^]'. 220 web0083.zxcs.nl ESMTP Exim 4.95 Sat, 23 Jul 2022 18:35:35 +0200 QUIT 221 web0083.zxcs.nl closing connection Connection closed by foreign host. So either that, or the server is checking some blacklist and deciding not to talk to you. It should never be necessary to talk to an MX on a port different than 25, so maybe if you try that they might even consider it fishy and block you (longer). Cheers.
