>I have a problem with a major danish ISP, that is
>running a setup where only customers can connect
>to their primary MX. All other SMTP servers are
>rejected and must reconnect to secondary.
First, that's an extremely poor and wasteful setup. It makes one wonder
whether or not they should even receive any mail. :)
If set up improperly, they won't get much of their mail. If set up
properly, they will get it, but with lots of bandwidth wasted. In their
case, they tie up TCP/IP connections on the server for 5 minutes, which
could in rare cases cause servers to crash. So they really need to get
their act together, and deserve to have late/missing E-mail.
>This does not work anymore:
>
>20020617 093959 127.0.0.1 SMTP (3024) Trying cool.dk (0)
>20020617 093959 127.0.0.1 SMTP (3024) Connect cool.dk
>[212.242.41.34:25] (1)
>20020617 094022 127.0.0.1 SMTP (3024)
>20020617 094022 127.0.0.1 SMTP (3024) SMTP_DELIV_FAILED
>
>There is no "MX connect fail" but a sort of timeout after ~20 seconds.
I can't explain why IMail is timing out after only 20 seconds. IMail is
required to wait 5 minutes (if I recall correctly) for the greeting, so I'm
guessing that IMail is getting something back (a "No TCP connections
allowed to port 25" type packet, for example). But, I can't explain why it
wouldn't go to the backup MX record.
> - Blocking their primary MX in our firewall.
> The only difference is that the SMTP_DELIV_FAILED
> now comes instantly. It seems that IMail just dont
> fall back to the secondary MX.
This would seem to support the theory that IMail isn't timing out, but
instead getting the "No TCP connections allowed to port 25" ICMP message.
> - Using the HOSTS file to switch the address of
> their primary MX to the more "friendly" servers.
> This works when pinging, but IMail persists using
> the original addresses even after rebooting. I
> don't have any idea why..
Note that you need to use the domain, not the hostname of the
mailserver. So in this case, you would need to add:
212.242.40.4 cool.dk
-Scott
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