--On March 21, 2006 2:11:31 PM -0500 Valdis Kletnieks 
<[log in to unmask]> wrote:

> On Tue, 21 Mar 2006 14:03:22 EST, Michael DeGregory said:
>
>> Is there anything specific we can look for when we sniff the port and
>> get a probe failure?
>
> Look for a *second* piece of mail coming back the other way that looks
> like a bounce message.
>
> Some sites are poorly set up, and will give a '250 OK' to essentially any
> address, including a bad one - and then send a bounce message when they
> discover the mailbox is in fact totally invalid.

I've seen a few horrendously broken auto-reply/vacation systems send a 
message back, while also sending one along to the user too.

>
> A better configuration is to have the box able to issue a 450/550 "no
> such user" error at the mail gateway - that way you get the benefit of:
>
> 1) You never have to accept and queue the mail for an invalid address.
> 2) If the MAIL FROM: is bogus (as it is for much spam), it means you don't
> end up trying to bounce the mail to a bogus address (or even worse, a
> legitimate address that has been joe-jobbed).
>



--
"Genius might be described as a supreme capacity for getting its possessors
into trouble of all kinds."
-- Samuel Butler