[SPAM-TAG] Re: [SURBL-Discuss] Another to whitelist

Jeff Chan jeffc at surbl.org
Thu May 27 03:12:31 CEST 2004


On Thursday, May 27, 2004, 2:02:06 AM, Jose Cruz wrote:
> Jeff Chan wrote:
>> On Wednesday, May 26, 2004, 3:16:45 PM, hans hans wrote:
>> 
>>>On Wed, 26 May 2004, Jeff Chan wrote:

>>>Another point or remark. At the surbl site it is mentioned that sendmail
>>>isn't aware of bodies. This isn't true for part of your conclusion. It is
>>>possible to check the body in sendmail but the problem is dat you will
>>>have to fetch the data block to do it. Then again, not getting spam in the
>>>users INBOX might also help.

>> Yes, milters can be used with sendmail to block on message
>> bodies, but as you note it requires letting the data through.
>> On the other hand regular RBLs can be used by the MTA to reject a
>> lot of connections directly based only on headers.  After passing
>> RBLs the bodies need to be checked, and doing that with an MTA
>> milter probably uses fewer resources than doing it in
>> SpamAssassin, for example.

>>>A little file to help understand the above:

>>>http://spamikaze.is-a-geek.org/sendmail-subjectblocking.txt

>>>Reading the SubjMatchReject file will produce a 550.

> Not really...

> SMTP protocol is based on a series of commands.

> - EHLO
> - MAIL FROM
> - RCPT TO
> - DATA

> Message body and ALL headers are inside DATA command. So, if you've 
> decided to block the message, based on the Subject Header content, the 
> MTA needs to receive ALL the message body, before sending the 550 answer 
> to the smtp client. Even if it seems to you you've already said to the 
> MTA that it shall reject the message. This isn't particular to sendmail, 
> but defined at RFCs.

Good point.  I forgot that Subject is in the message body and not
the headers as far as SMTP is concerned.  Subject is only
apparently included with the headers by MUAs.  So if you've got
the Subject line you could also process the rest of the body with
SURBLs.

Jeff C.



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