I've been recently migrating from an exchange 2003 to 2010 system, currently running in co-existence. I'm slowly moving my mailboxes over to the new 2010 box.
Every few days or so (maybe once a week) I have an issue where the SMTP connector or routing group between my old 2003 and new 2010 server seems to drop out. ANy email sent to a user on the new box, and organization either from outside the organization or from the old server, the messages end up in a queue as unreachable.
I end up needing to reboot the new server and everything come sup just fine. I attempted to restart the information store service, but it just hangs.