[Mimedefang] DNS and MX records

[Kris Deugau]

netguy wrote:
> Receintly I updated DNS for a few domains.  My registrar gives the 
> option of assigning an IP addy for domain.tld without having an alias: 
> mail.domain.tld  Ok, says I, lets give it a go.  Bam!  Slam, Spam 
> started invading my privacy.  This leads me to believe either:
>    1. Mail ( spam ) in this case is being sent to domain names without 
> doing MX lookups.

Yep.  Spamware will certainly blindly open a connection to port 25 on 
<domain.tld>, rather than sorting through MX records.  Personally, I 
think it's "better" to have that A record in place, spam notwithstanding.

Garbage is spewed out to <dictionary words>@<domain.tld> - for a time, 
it looked to me as if some ratware was actually literally iterating 
through ALL possible usernames composed of a-z and 0-9.  If you've got a 
catch-all address, you may want to rethink that.  If you're running 
MIMEDefang, you may want to look into fleshing out filter_recipient().

-kgd