Setting up a second exchange server in the same routing group, all installed fine, however, after moving a mailbox to the new server and then sending an email to the mailbox, the mail got stuck in the queue on the first server.
Checked the common things like DNS, firewall ports etc. all looked fine. But still the mail would not go, also tried to send a mail from the new mailbox to a mailbox on the old server. Still no joy.
The two servers where on separate networks, with a Cisco 857 ADSL router at each site and a IPSec site to site VPN between them. Full all open IP access allowed from each server to each other. Couldn’t see the problem.
Then I found this from Microsoft: http://support.microsoft.com/kb/919091
Cause 5 – The IP inspect rule, on each of the routers I had one for SMTP. This appeared to be blocking an SMTP verb or something and causing the connection to stall with this strange error in the queue viewer on each server: the semaphore timeout period has expired.
Solution: I removed the IP Inspect rule from each router, (you will still probably need a tcp inspect to allow outbound smtp to the net. Rebooted the routers, and restarted smtp on each exchange server (just to be sure) and hey presto. Mails started to flow.
Now i can see about setting up a routing group connector!