On 29/07/20 9:54 am, Michael Wyraz wrote:
Hello Wietse,
thank you for the response. I tried to find the correct section in RFCs
that describes this but I did not find the place where it defines that a
EHLO cannot be answered with a 550
Can you point me to the right RFC section?
It can be, but iit has a different meaning here. RFC5321 5.3.2 states:
EHLO or HELO
S: 250
E: 504 (a conforming implementation could return this code only
in fairly obscure cases), 550, 502 (permitted only with an old-
style server that does not support EHLO)
So Postfix assumes that the 550 means that the server does not support
EHLO and falls back to HELO as a result (which you can see happening).
The remote server then hangs up unexpectedly and so postfix assumes that
the connection got dropped and appropriately defers the message to retry
it later.
So Postfix is absolutely conforming to RFCs, the remote server errs by
(1) returning the wrong code in response to EHLO (unless they really
don't support EHLO) and (2) hanging up prematurely.
Peter
