Vista, Oulook 2007 IMAP

I have a Vista test machine with Outlook 2007 configured for Secure IMAP
(port 993) to my Exchange 2003 server. Testing the machine outside of our
network, the IMAP connection does not connect. Looking at my border firewall
logs, it seems that it is also trying to connect to my email server on port
365 UDP. I could just let the port through the firewall, but I'd like to know
whats its doing first...

Outlook 2007 on a WindowsXP machine with the same Secure IMAP setup works
fine however outside our network.

What is Vista trying to connect to over port 365 UDP with Outlook 2007?

Thanks!