Re: [SLE] SMTP authentication

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The Saturday 2006-04-29 at 13:19 +0200, Hylton Conacher (ZR1HPC) wrote:

understand an SMTP server must send its load to another SMTP server. To
clarify let us assume there are only 3 SMTP servers in the world ie my local
one, my ISP's one, the destination one.

Me-- |A|----------Broken link--------------|B|
\ /
\---------Link OK-------|C|--------/


[A]
Mozilla ----- local----\---------------------- Destination [B]
\ postfix \ / SMTP
\ \ [C] /
-------------------ISP ---------/
SMTP

Those are the possibilities.

Let us assume that A cannot see the destination B. It determines that the
alternate path to B is via C.

It's rather that you tell it to do it that way; it doesn't do it
automatically. The route is decided looking at its configuration and the
answers from the DNS.


The destination (B) does not need to authenticate the messages it receives

It doesn't because it is the SMTP server responsible to receive email for
the domain in the "To" field. Ie, it is not a relay, but the final
destination.

however C does. So while my local SMTP server is connected and sending mail to
C, C does authentication and sees that the FROM header in some of the emails
is not the same as the email address as the person logged onto the ISP. C
therefore drops those messages into the forever ether. The messages whose FROM
header is the same as the person dialed in are relayed to the destination
server (B).

Well, that's because the person administering that crappy server has
decided to do it that way, IMO. I know it happens.

It should, however, never "drop" mail, but "reject" mail. That's very
irresponsible on their part.


Can the above happen to a local SMTP server (A) as it has been happening to Me
when I sent email directly from my Mozilla Mail to C. If the FROM header in
some of the emails is not the same as the email address as the person logged
onto the ISP. C therefore drops those messages into the forever ether. The
messages whose FROM header is the same as the person dialed in are relayed to
the destination server (B).

I prefer to send through (A) because that way I see the logs, and reading
them I know what is happening. If I get a rejection, I know it, not a box
popping up from mozilla telling me of a error in transmission. I get more
control.

However, you can tell (A) to send directly to (B). That's what I normally
do. It works with SuSE lists, but it doesn't with some other recipients:
they check that (A) is on a dynamic address and refuse talking.

- --
Cheers,
Carlos Robinson

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