Webone blocking port 25??

Matthew Hawkins matt at mh.dropbear.id.au
Fri Jul 26 15:25:46 EST 2002

Martijn van Oosterhout (kleptog at svana.org) wrote:
[--- snip ---]
> MAIL FROM: martijn at fake.mail.address
[--- snip ---]
> 550 rejected: cannot route to sender <martijn at fake.mail.address>

That's the envelope sender, not the message header sender (which we were
discussing).  What makes the envelope more valid is the fact its created
by a remote MTA, not a person.  Not that it's impervious to forgery, but
people tend to need an idea of SMTP to do so, which rules out 99% of
internet users.

Alfred (alfred at mazuma.net.au) wrote:
> It probably does the rejection AFTER the data because you can have an 
> arbitary list of to address, some which may work and some which done. 
> You only do a 550 (or any 5xx) code on fatal errors.

Yet another person possibly confusing envelope and message header

I believe the real reason for doing it at the end is that some MTA
software behaves... differently.  Some even behave outright wrong.
Dealing with all the special cases so you don't screw your own MTA
software over in the process is an art form.

It's possibly more expedient to do all your processing at the end when
you have all the information available to you (client address, envelope
sender, envelope recipient, message data) so perhaps exim chooses to do
it that way by design.

"So, logically, if she weighs the same as a duck, she's made of wood, and therefore a witch!"
(Monty Python and the Holy Grail)

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