DragonFly BSD
DragonFly kernel List (threaded) for 2004-01
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Spam issues in DFly lists

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 21 Jan 2004 10:39:47 -0800 (PST)

    This is just a head's up... the command channel for some of the
    dragonfly lists is starting to get random spam.

    It's probably just a matter of time before the posting channel starts to
    get it, at which point I will have to turn the spam filter on for the
    dragonflybsd.org domain.

    I am going to try to avoid turning on the 'only a subscriber can post'
    feature of the list server, because I think it's anti-social, but
    the filter I will use does a number of checks.

    To test whether the spam filter would block your emails, simply send an
    email to test@xxxxxxxxxxxxxx  This goes into a sink/null so you will not
    get a reply.  If you do not get a bounce you are ok.  If you do get a
    bounce then the spam filter has got you by the throat :-).

    Basically the spam filter requires:

	* Reverse DNS must resolve.

	* Reverse cannot resolve to a cablemodem or DSL domain name 
	  (I do this with a wildcard compare against ISP's that I get
	  spam from). 

	  If you have your own personal domain and the reverse points to
	  it, you should be fine.

	  If you get a bounce due to this, you should be able to send mail
	  by pointing your SMTP to your ISP's SMTP server instead of 
	  trying to make direct connections to the target domain.

	  If that bounces I can probably adjust my list to compensate, 
	  unless the ISP is the source of a huge amount of spam sent 
	  through its own servers.

	* Envelope from address must resolve.  The spam filter makes a
	  reverse connection (as if it were sending mail back to the From
	  address) to test the address.  If the RCPT succeeds it's happy,
	  if it doesn't, the mail is rejected.  No actual email is sent,
	  it RSET's the connection after testing the address.

    The filter gets about 80% of the spam that comes into my other domains
    and is fairly non-intrusive except for the occassional person who is
    trying to run a personal SMTP server off their dsl or cablemodem line
    without setting it up to forward to their ISP's mail server.


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