[ On Saturday, March 29, 2003 at 21:22:35 (+0100), David Saez wrote: ]
> Subject: Re: [Exim] sender callout failing
>
> I mainly want to test the addresses as most spammers use inexistent
> return addresses. It will cut almost 20% of all received spam, but i
> cannot use it for that purpose as some non spam emails come with email
> addresses in the header (mainly From:) where the mx for the
> corresponding
> domain does not accept null envelope senders. I don't need to test that
> condition, I only need to test if the address exists or not.
Either you're testing the sender address (i.e. the return address, also
known as the SMTP envelope sender address, a.k.a. the parameter given to
the "MAIL" command), or you're not. This is only one sender address.
Forget the address(es) in the "From:" header! Forget all the headers!
SMTP servers should not ever examine the addresses in the RFC-[2]822
headers in the _body_ of the message!
It's fine to validate the SMTP envelope sender address, but that's all.
Note though that active validation of sender addresses by pretending to
send a test message to them is very problematic and will cause
unexpected problems and strange behaviour. You should try to restrict
your tests to validating through the DNS alone.
If all you want to do is filter spam then you can do whatever checks you
want _after_ the SMTP transaction is complete -- i.e. do them in/through
your local delivery agent!
> > A server that won't accept bounce messages _is_ broken and _all_ sender
> > addresses routed to that server are, _by_definition_, invalid!
>
> no, the server is broken, but it can receive email for valid addresses.
Sorry, but you're missing this most important point:
A server that refuses to accept bounces will not ever accept return mail
for any _sender_ address!
Think about it. Think about it very carefully. Think about it by
answering the question: When is the only time the sender address ever
used?
The sole purpose of the SMTP envelope sender address is for sending
return bounces. If the server responsible for a sender address refuses
to accept bounces then that sender address is, _by_definition_, invalid!
--
Greg A. Woods
+1 416 218-0098; <g.a.woods@???>; <woods@???>
Planix, Inc. <woods@???>; VE3TCP; Secrets of the Weird <woods@???>
