[Cialug] Sendmail spam rejection

[Dave Weis]

We have a Barracuda that does this very well. It attempts an SMTP 
connection to the backend server when it sees a new address.

On Tue, 24 Oct 2006, Daniel A. Ramaley wrote:

> I have what is hopefully an easy question for the sendmail wizards on
> this list. I have 2 mail servers. The first receives mail from the
> outside world, filters out most of the spam, and then passes the mail
> to the second server (which is what users actually log in to to check
> their mail). The first server runs sendmail. It does not currently have
> a way to verify the recipient addresses, so it just accepts all mail
> for the domain. Then when the first server forwards mail on to the
> second server, any invalid recipients cause a bounce to be generated.
>
> I would prefer for the first server to never accept invalid recipients
> in the first place, before running expensive spam checks and clogging
> up the second server with bounces that usually never go anywhere. I
> have a nightly data feed with a list of valid recipients. What is the
> best way to load that list on to the first mail server and make
> sendmail check it as soon as it has received a recipient address?
>
>
> So far Google has not been quite as helpful as i would have liked
> (probably because i'm not familiar enough with sendmail to search the
> correct terms), but i've found 2 possibilities. I don't know whether
> they are plausible, though. One would be to set up a virtusertable hash
> file with a list of valid recipients (all 20 000 of them), but i think
> that is mostly used to rewrite addresses. I don't want to rewrite
> addresses, i just want to have a list of valid ones and deny the rest:
>    user1 at example.com    user1 at example.com
>    user2 at example.com    user2 at example.com
>    ...
>    @example.com         error:"550 We do not accept spam"
>
> Would that work? If not, the other idea i've seen would be to set up
> sendmail's ldap_routing feature, but instead of using real LDAP, use a
> hash table. Unfortunately, i've not yet found understandable
> instructions on how to use the ldap_routing with a hash file.
>
> ------------------------------------------------------------------------
> Dan Ramaley                            Dial Center 118, Drake University
> Network Programmer/Analyst             2407 Carpenter Ave
> +1 515 271-4540                        Des Moines IA 50311 USA
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-- 
Dave Weis
djweis at internetsolver.com
http://www.internetsolver.com/