Messages staying in "unreachable destination"


We appear to be having a bit of an issue with our Exchange 2000 server. All of a sudden messages are not going form our exchange server to our relay server. They are sitting in microsoft Exchange queue under "unreachable destination".

If the server is rebooted then this allows for the messages to go through. but it appears to stop again at a random period of time later. There appears to be nothing changed on either the Exchange system or the relay server in the DMZ.

Anyone else experienced this or have any ideas of what i can do to try and fix it?

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NetminderConnect With a Mentor Commented:
PAQed, with points refunded (125)

EE Admin
Have you recently performed an upgrade or migration?

If you enumerate the messages in the "unreachable destination" queue and open one up, what is the address that it is trying to send the email to?    This is of key importance!

I've seen the same problem many times - let me know what you find in the queue.
monkeyspunkAuthor Commented:
knikkij - Its somewhat of an odd one, as appears to be any messages, Ive enumerated them and it doesnt appear to be one destination which is quite odd, as that was what i thought was the problem.

As for upgrade or migrations, there has been no major upgrades or migrations done as such, however some security fixes were installed on the relay that Exchange server forwards all mail to.

The "problem" I have now is that the server seems to be fine at the minute. It has not had this problem for just under a week now, and the only thing i can thing of is that I applied some security fixes to the exchange box to bring it inline with the relay server. Now that I can't replicate the problem it's hard to further diagnose, but Ive switched on lots of logging for the smtp engine amongst other things to try and give me some more diagnostic capabilities should it go again.

Any further ideas on what could have caused it to get into that routine?

Many Thanks
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We had some major major issues after someone ran the IIS Lockdown / URLScan utility on the Exchange server that took us eighteen hours with Microsoft to correct.  That's a nasty little tool - and I'm convinced the URLScan was secretly snuck into a security rollup - but that may just be the conspirator in me.

Messages unreachable (obviously) means it's an invalid address.  We see this often after migrating users from 5.5 to 2000 when people reply to old 5.5 addresses (that's when you see IMCEA in the message destination).

When you looked at the messages in the queue, however, they did look like valid SMTP addresses, correct?  Were they internal or external or both?

Can you look up and see which security patches you applied on the Exchange server?  I think it would be marvelous to figure out the root cause on this one.
monkeyspunkAuthor Commented:
Hi knikkij,

The messages that get stuck are just for outbound messages, which is what made it even stranger all internal mail traffice was still working fine. As for the messages, they did all seem to contain valid addresses and most of them i could trace to people that we are regularly in contact with.

However what i did notice only once, out of the several times the messages got stuck was that there were two messages that didnt appear to have any destination?!? Now whether they were there at all times and it only enumerated enough to show me the first 100 that had got to the queue or not i don't know.

As for the patches I will have a look and see which ones were applied and the fact that since then it appears to be ok.
Problem appears to have been resolved after the author updated the service packs on the relay server - beyond that we didn't find any major configuration errors.
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