Mail delivery wierdness

[Ryan Thompson]

keith at smmc.qld.edu.au wrote to Free bsd :

> Hi all,
> I am trying to connect to an exchange server via my new gateway ipfilter
> fbsd 4.7 ipnat firewall.
> Telnetting to the server inside to port 25 reveals...
>
> Connected to 203.44.yyy.xx
> Escape character is ']'.
> Connection closed by foreign host.
>
> Why would it close instantly?

That's usually the behaviour indicating that there is a server at
203.44.yyy.xx, but there is no service listening on port 25. (Or, maybe
your fancy ipfilter firewall is simulating the equivalent).

The first thing you should do is confirm that the server in question
*is* actually listening on port 25. MS Exchange is pretty far beyond the
charter of this list, but general network techniques would still apply:

Try the same telnet test using the win32 telnet on the server itself.
(i.e., telnet localhost:25, and try it by the public IP in case Exchange
isn't listening on localhost for some reason). If it won't talk SMTP
with you in either case, you won't get any farther. On the other hand,
if the test is successful, try the same thing from the next hop (your
FreeBSD gateway?).

If you isolate the problem to the gateway (and/or every host directly
connected to the other side of your gateway), you'd probably do well to
forward your firewall rules and ipnat config to the list (as well as a
description of what you're trying to accomplish with your config), in
which case we'll be able to give you better specific instructions.

> Does this reveal while I can't send mail to any email account on it?
> Is this an exchange hassle? Is port 25 to be only tcp or udp as well.

SMTP is a connection-oriented service.  SMTP can, in theory, be used
over transport layers other than TCP, but SMTP over UDP would require a
fair hack to SMTP to implement. So, the short answer is, forget about
UDP. :-)

- Ryan

-- 
  Ryan Thompson <ryan at sasknow.com>

  SaskNow Technologies - http://www.sasknow.com
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