[afnog] Fighting SPAM

[SM]

At 03:04 05-09-2008, Maina Noah wrote:
>I have this mail systems that i just brought up for a client couple 
>of days ago.
>The MTA of choice was Postfix and Dovecot for IMAP/POP stuff. I also
>complied Spamassassin for handling spam on this system. The OS is 
>Linux Centos 5.
>
>However the flow of junk and spam email to the users Inbox is so huge.
>
>I have fine tuned spamassassin to the best of my knowledge and it seems to
>work fine however, i am not certain if it is really blocking spam 
>emails all at.

SpamAssassin does not block spam; it only rates the contents of the 
message.  It is up to the software calling SpamAssassin to take 
action.  If that software is interacting with the SMTP session, it 
can reject the message.  There is a Dovecot plugin that can move 
messages tagged as spam to an IMAP folder.

>Emails from the domain in question sent to yahoo and gmail tend to 
>go to the yahoo/gmail spam folders
>of the recipients, instead of the Inbox.

That is a different issue.  You have to contact these providers and 
find out why your email is considered as spam.  Generally, it's 
because the email is not formatted correctly or the mail server is a 
known source of abuse.  If the mail server is incorrectly configured, 
i.e. hostname, Return-path used in the outgoing email etc., it can 
lead to delivery problems.

>See below the sample output of the /var/log/maillog file from the same server.

According to the log, the message is being identified as spam.  In 
your existing setup, you have to configure Dovecot to take action, 
i.e. move the message to a different folder instead of delivering it 
to the INBOX.  The better solution would be to integrate software 
(Amavisd-new, MIMEdefang etc.) with Postfix so that the spam can be 
rejected during the SMTP session.

Regards,
-sm