[NTLUG:Discuss] Sendmail question

[Richard Cobbe]

Stephen Klein wrote on 9-5-1999:

> "Gregory A. Edwards" wrote:
> > 
> > In trying to get sendmail to masquerade my public domain from an internal
> > host I've got all my local domain names being rewritten but why do some
> > ISPs still reject with the following message:
> > 
> >    ----- Transcript of session follows -----
> > ... while talking to smtp4.jps.net.:
> > >>> MAIL From:<greg at eagle.newage.local> SIZE=381
> > <<< 501 <greg at eagle.newage.local>... Sender domain must exist
> > 
> > Greg E
> > 
> > _______________________________________________
> > http://ntlug.org/mailman/listinfo/discuss
> 
> 
> It's an anti-spam block that some ISP's use.  Most SPAMer's use fake
> domains to get around some spam filters that block based on the domain
> name.  Basically, the recieving mail server does a DNS lookup and
> rejects the e-mail message if the lookup fails.  Cyberramp (My former
> ISP, dang IA!) did this because they were having trouble with SPAM
> clogging their mail servers.

Pretty much, yep.  I dealt with this some time ago myself.  If you've got
sendmail-cf installed, then add the following two lines to your .mc file
and regenerate sendmail.cf:

MASQUERADE_AS(hex.net)
FEATURE(`masquerade_envelope')

(replacing hex.net with your ISP's address, obviously)

I suspect that what you're missing is the masquerade_envelope line.  I'm
not entirely sure what this does, but I think it also does name
masquerading in some of the headers that MASQUERADE_AS doesn't affect by
default.  For more info, check out

http://www.sendmail.org/m4/masquerading.html

HTH,

Richard