Date: Thu, 5 Dec 2002 17:32:28 +0000 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: FreeBSD Chat <freebsd-chat@FreeBSD.ORG> Subject: Re: Mail Insanity Message-ID: <20021205173228.GA93795@happy-idiot-talk.infracaninophi> In-Reply-To: <3DEF75D7.9040401@centtech.com> References: <3DEF75D7.9040401@centtech.com>
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On Thu, Dec 05, 2002 at 09:50:47AM -0600, Eric Anderson wrote:
> I think I'm going to go insane.
>
> The spammers of the world have been sending mail to (insert made up name
> here)@mydomain.com, causing my sendmail to respond to them with "No such
> user", which bounces BACK to me since they are using a fake address,
> which ends up in my inbox (I am postmaster). I'm getting about 1000 per
> day, and can't take it anymore..
>
> Anyone found a solution for this?
Hmmm... sendmail should reject messages based on the MAIL FROM:
parameters if the sender address given is unresolvable. I guess that
means the spammers are forging messages using valid addresses...
sendmail has tcp_wrappers functionality compiled into it on FreeBSD,
so how about a rule like:
sendmail : PARANOID : RFC931 20 : deny
in your /etc/hosts.allow ? That should cause sendmail to reject the
attempted connection from any IP number with an unresolvable domain
very early in the SMTP dialog.
If you use FEATURE(`access_db') you can blacklist the netblocks used
by the spammers, or you might find it more profitable to use something
like DUL (http://mail-abuse.org/dul/ -- pay-for nowadays, bah!, or
OSDUL (dialups.relays.osirusoft.com) --- plenty of DNS blocklists at
http://moensted.dk/spam/) to prevent e-mails directly from netblocks
used by dialups. Finally, there's FEATURE(`blacklist_recipients')
that you could put into your sendmail.mc, which lets you reject
messages (via the access db) based on the local addressee.
The anti-spam section in /usr/share/sendmail/cf/README is well worth a
read.
Cheers,
Matthew
--
Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks
Savill Way
Marlow
Tel: +44 1628 476614 Bucks., SL7 1TH UK
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