sender verification

[Alex Neuman van der Hans]

Any good links/faq's you can recommend on accomplishing these feats with
exim4 on Debian?

-----Original Message-----
From: MailScanner mailing list [mailto:MAILSCANNER at JISCMAIL.AC.UK] On Behalf
Of Jim Holland
Sent: Wednesday, May 11, 2005 2:42 AM
To: MAILSCANNER at JISCMAIL.AC.UK
Subject: Re: sender verification

Hi Jan-Peter

On Wed, 11 May 2005, Jan-Peter Koopmann wrote:

> > That is why I would
> > like to see this being implemented after receipt of the message -
> > just as DNSBL and other checks are carried out afterwards by
> > MailScanner.
>
> I use DNSBL at MTA level and with SpamAssassin. If the IP triggers one
> of two RBLs I trust the message is rejected. If it hits one of several
> other RBLs I slow down the SMTP protocol (enforcing synchronization)
> and catch quite a lot of spam with that.

I am not familiar with how to slow down the SMTP connection selectively - I
don't think this is a feature that sendmail offers.

> To be honest: I would think of this as unneccessary overhead. Why
> don't you simply verify the sender address at MTA level, add a header
> to the message in case the verify fails and then write a simple
> SpamAssassin rule for this? That's what we do here. It's quick and no
> code has to be changed. I'm not sure how easy this is with sendmail
> but with exim this is a matter of minutes.

Again, I don't know of any easy method of doing this with sendmail without
writing a special milter.

> New code in MailScanner only brings the possibility of new errors as
> the code gets more and more complex, especially since the feature you
> want would mean implementing/using SMTP. The only advantage would be
> that people not using SpamAssassin could use this functionality. I
> doubt there are many people out there that fit this definition though.
> :-)

Sadly I am in fact in this category.  The current server could not cope.
However there is a new server sitting on my desk that I have just loaded
with CentOS (RHEL4 clone).  Now to try Exim, SpamAssassin etc . . .

Thanks for your feedback.

Regards

Jim Holland
System Administrator
MANGO - Zimbabwe's non-profit e-mail service

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