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Intermittant "Unreachable Destination" Problem

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Intermittant "Unreachable Destination" Problem - 13.Mar.2007 1:33:17 PM

djmarkm

Posts: 1
Joined: 12.Mar.2007
Status: offline

Hi
We are having a bit of an intermittant problem with outbound mail
delivery on a SBS2000 (Exchange 2000)
This server has been in place for 4 years with no real issues so far.
However the following problem has now occurred twice in one week and
the only way we can clear it is by rebooting the server.

Setup:
SBS 2000 - 1 internal network card (192.168.1.1) and the external
connection (with external IP address). ISA Server is installed in
Firewall mode.
Incomming mail is collected by Exchange from a POP3 mailbox on the
internet using the POP3 connector.
Outging mail is handed over to the ISP's smtp server (ie:
relay.ispname.net) via an SMTP connector. (We can't really use DNS
deliver as many SMTP servers are now blacklisting private IP
addresses)

Issue:
Client complains no outgoing mail is being delivered. I check the
queues on the default SMTP Virtual server to find all the outbound mail stuck
in the "Unreachable Destination" queue.
There is also a queue for the SMTP connector which says 'Retyring' and
when you right click this and choose properties, the status says "DNS
Error"
However I am able to open up a command window and ping the ISP's SMTP
server ok (ie the name gets resolved correctly and is reachable) I am
also able to browse the internet without issue. As a test I also
configured Outlook Express to send mail out directly to the ISP's SMTP
server from the SBS2000 machine. This works fine which is indicating
to me that there is no problem with connectivity or DNS.

I've tried stopping and starting the SMTP Virtual Server. Deleteing
and recreating the SMTP connector and even adding a second SMTP
connector to another SMTP mail server that we are permitted to relay
through. All with no luck.
The only way we have to resolve this is to reboot the server. Upon
reboot, the error clears and the queue is sent.
.. until the next time the error occurs.

Does anyone have ANY ideas at all on this?
Thanks

Mark