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Re: [LUG] email

 

On Thu, Jun 25, 2009 at 01:26:08PM +0100, Mick Vaites wrote:
> Most individuals with their own mailservers (on dsl lines most likely) don't
> run MX's they use smart hosts or backup MX's with their ISP. Eitherway
> neither the smarthost nor the backup MX has any knowledge of whether an
> email address at the domain exists.
> 
> So the bounce comes back from daemon@xxxxxxxxxx to fake(s)@yourdomain.com.
> Smarthost trys to deliver this to your server and you respond "no such user"
> so the smart host sends a response back to daemon@xxxxxxxxxx "no such user".
> (Consider you could also have smart hosts at both ends ... Yuk).

Um? Surely a smarthost is only for clients to send to, probably
authenticated, not accepting mail from the internet in general.

I don’t know if there’s a huge amount of value to having a backup MX
nowadays, but I’d suggest it shouldn’t be sending a no-such-user message
back to the sending host, since this will probably lead to backscatter
if the spammer has faked the from address (of course, nobody would
actually do that, would they?).

> So if a person is plagued with spam email or having their domain hijacked by
> a spammer or dictionary attacked - how can this be better (and less resource
> intensive) than sending an email to the bit bin if it's incorrectly
> addressed ?

If you’re accepting spam mail at all when you don’t have to, you’re
doing it wrong. This means no accepting mail for addresses you know
aren’t in use, and that’s exactly why I don’t really think backup MXes
are worth the trouble these days.

> I'm sorry but "best practices" are just that and there will always be
> exceptions.
> 
> I've been following a customers exchange server overnight which was taken
> offline "no such user" responses. Yes maybe they shouldn't be building
> exchange servers that cannot cope with thousands of "no such user" messages
> -- but unfortunately there are loads of boxes out there just like this one.

Exchange in “doing it wrong” shocker. ;)

-- 
Benjamin M. A'Lee || mail: bma@xxxxxxxxxxxxxx
web: http://subvert.org.uk/~bma/ || gpg: 0xBB6D2FA0
“I am somehow less interested in the weight and convolutions of Einstein’s
brain than in the near certainty that people of equal talent have lived and died
in cotton fields and sweatshops.” — Stephen J. Gould

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