Am 12.06.2020 um 04:43 schrieb Adi Pircalabu:
First thing first, this isn't necessary a Dovecot related thread and
yeah, and i'm sorry for that. Just thought to give some information on
an issue that actually turns out to be completely out-dated.
using a challenge-response system like the one suggested by the
initiator ("click here if you're not yet another bloody SEO guru") is
plain wrong for several reasons,
full ack
$ telnet server 25
Trying x.x.x.x...
Connected to server
Escape character is '^]'.
220-server ESMTP Postfix <=== Postscreen trap here ;)
220 server ESMTP Postfix
HELO client.domain.com
250 server
MAIL FROM:<>
250 2.1.0 Ok
RCPT TO:<vic...@domain.com>
250 2.1.5 Ok
DATA
354 End data with <CR><LF>.<CR><LF>
From: Me
To: You
Subject: Test
SA GTube string here
.
550 5.7.1 Blocked, see you later.
QUIT
221 2.0.0 Bye
Connection closed by foreign host.
In this case the rejection comes after DATA, a content filter should be
able to return either 4xx or 5xx *after* swallowing the entire email.
I know and I already tried out such a filtering long before. With lots
of problems and long discussions to mailadmins of large providers. The
result: specifications and reality do not always match. :-)
Maybe, and I really hope so, this problem no longer exists. I will
immediately reconfigure my mail system, if rejecting mails after DATA
will be safe and reliable nowadays.
Rejecting or deferring after DATA is perfectly fine these days. If the
sending MTA, acting as a client in the SMTP conversation, doesn't behave
properly to 5xx after DATA, it's not the recipient's MTA problem, the
sender is broken and there's nothing the receiving MTA can do about it.
Make it their problem, not yours.
Okay, makes sense!
/ Andreas
