said by Leathal 
:Yes I am using MAPI, but Outlook 2007 is a completely different application out of the box. With outlook 2003 I don't get the error, so MS obviously changed how Outlook 2007 operates.
Yes the cert for OWA is the EXACT host name on the A record published in DNS, it works perfectly from the outside, the inside is where it gives me problems even though we have the domain.com zone in our Windows DNS server with the host record for OWA which translates fine when you look at it nslookup.
From what I have heard it maybe due to having to setup an internal Cert on Exchange 2007 x64, I can't remember the shell command for it now.
Leathal
OL2007 isn't different except that it will use autodiscover to create the MAPI profile and may fail if your autodiscover website and accompanying certs and DNS entries aren't correct. Once the MAPI profile is setup (which you can do manually from inside the firewall), then connecting is exactly the same as OL2003. 
