SMTP errors after enabling RBL

A short while ago I enabled RBL in my home servers’ configuration. It rejects several messages a day, but some with strange side effects. It always looks like this:

04/03/2003 07:07:01 PM SMTP Server [01955:00007-65541] 554 Your host 195.223.38.66 was found on an RBL blacklist. This means your SMTP server is not configured properly. Please contact a system administrator to correct this situation. Thank you.

04/03/2003 07:07:02 PM SMTP Server [01955:00007-65541] 503 Issue MAIL FROM: command before RCPT TO: command

04/03/2003 07:07:03 PM SMTP Server [01955:00007-65541] 503 Issue RCPT TO: command before DATA command

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “Message-ID: d53cb4d58e30$f1d16c3e$be6d99f3@kldgyvdhyb.l” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “From: “Margot Merlino” margotmerlino@paris.com” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “To: my@domain.net” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “Subject: Think you’re good at poker? 9256ebJU5-379d-13” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “Date: Thu, 03 Apr 2003 07:48:43 -0300” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “MIME-Version: 1.0” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “Content-Type: text/plain;” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command " charset=“iso-8859-1"” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “X-Priority: 3” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “X-MSMail-Priority: Normal” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “X-Mailer: Microsoft Outlook, Build 10.0.2616” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “Content-Transfer-Encoding: base64” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “UGxheSBZb3VyIEZhdm91cml0ZSBQb2tlciBHYW1lcyBIZXJlDQoNCg0KVGly” unrecognized

(removed lots of similar lines - Gerco)

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “LXJlbW92ZS5jZ2kNCg0KDQoNCg0KDQoNCmsyczENCg0KODM0MFJYbUM3LThs” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “MTA=” unrecognized

04/03/2003 07:07:04 PM SMTP Server [01955:00007-65541] 500 Syntax error, command “.” unrecognized

I do not really have a problem with this because it only seems to happen to messages that got rejected by an RBL, but I’d like to understand why this happens. It looks like the Domino SMTP server ‘forgets’ the first SMTP command because it has rejected the incoming message, and therefore the other commands are not received properly. Does anyone have more insight? I’ll set SMTPDebug= 2 in the notes.ini, see if I can catch the exact moment this happens.

Subject: SMTP errors after enabling RBL

Hi Gerco

This is classic spammer tactics. If he detects a server that will accept ESMTP pipelining, he just crams an entire SMTP “conversation” into a single packet and disconnects, ignoring any 5xx response codes.

Actually, quite a few spammers will attempt to pipeline messages even when the server has not responded with 250 PIPELINING after an EHLO.

Some discussion on this type of issue here - http://tinyurl.com/8t3r

Solutions:

1 - ignore and put up with it

2 - turn off inbound pipelining (this worked for me)

HTH

Subject: useful info, tnx!