denying email from your own domain but external IP's?

[Furnish, Trever G]

That's exactly what SPF is for:
http://spf.pobox.com/

You can hook it into sendmail as a milter (but I had lots of memory leak
problems that way, probably due to bugs in the perl threading library it
uses - YMMV):
http://spf.pobox.com/downloads.html

...or you can let SpamAssassin do the spf checks for you (and you should
only do these in one place, the MTA or SpamAssassin, not both, to avoid
needlessly doing the same DNS lookups twice).

You'll have to publish TXT entries for your domains (and subdomains -
consider using a wildcard entry).  This wizard can help figure that out:
http://spf.pobox.com/wizard.html

If you have addresses hosted in your domain(s) which you then forward to
different domains, that will run the risk of breaking with vanilla SPF.
To deal with that you need to use "SRS" in addition to SPF - haven't
done that personally, can't help there.

HTH.
 

> -----Original Message-----
> From: MailScanner mailing list 
> [mailto:MAILSCANNER at JISCMAIL.AC.UK] On Behalf Of Matt Kehler
> Sent: Thursday, June 30, 2005 8:31 PM
> To: MAILSCANNER at JISCMAIL.AC.UK
> Subject: denying email from your own domain but external IP's?
> 
> I'd like to toss all email if the 'from' address is of my own 
> domain (xyz.com), and it does NOT originate from my internal 
> 192.168.1.0/24 network.  Can I do this with MailScanner?  Or 
> can I even do it with Sendmail itself instead?  
> 
> Basically in our environment, people can use our internal 
> mail client while at work, or they can use our webmail, but 
> thats IT.  (ie, no Outlook express clients at home :).  So 
> essentially anything with the 'from' as xyz.com and NOT using 
> our internal IP addressing would have to be forged.
> 
> thanks
> Matt
> 
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