Re: Mail relay question

[Aaron Howell <aaron_howell () ngenuity-is com>]

Nick Vaernhoej wrote:
> I should have been more clear, I consider it spam due to my leaning
> towards not being open to relay.
> The vast majority of the spam appears to be returned email because the
> destination domain doesn't have a recipient for the email.
> The (spoofed) originator of the returned email is giberish or random
> names @myhomedomain.com

Ok, so that isn't spam, it's what we call "backscatter", and I think one
of the other responses in this thread pointed you in the appropriate
direction to find out what that means. If not, google knows...

> I guess knowing the little I do about email mechanisms I don't
> understand why the IP of the connecting client can craft an email FROM a
> domain the IP does not resolve to?

If this were the case, sending email would be a lot harder. Consider
vhosts. I may have one IP address hosting 10,000 domains. For forward
DNS, this is easy, ask for a name, get an IP address. But when I ask for
a reverse lookup, how do I know which domain to return?

> Makes sense, I have three domain names pointing home. The one behind 95%
> or so of the spam is one I have yet to really do anything with.
> Maybe it used to belong to someone else? But that would make the emails
> more specific to past owner I would think....

Given that one of the popular ways to try and deliver spam is to connect
to a mail server, then try to deliver mail to every name in
$HUGE_DICTIONARY_LIST, it would not surprise me at all to have a domain
with no actual email accounts associated with it receiving spam.

> Depends, my thought was that my wife will trust anything sent to her as
> long as it appears to come from me.

This is WAY outside the scope of this discussion, because now you're
talking about a whole different problem. Mainly, that users typically
trust what they see in their mail client/web browser/etc. This is one
reason why phishing attacks are still so successful, and we still have
networks compromised because JessicaAlbaNaked!!!one!.exe was sent by a
close trusted friend.

If you're really that worried about it, look into PGP/GnuPG and start
signing all your messages, and teach her how to verify the signature, or
get a free personal cert from Thawte...

-- 
Aaron Howell
nGenuity Information Services
509-396-2075 x6000

http://www.ngenuity-is.com