Hi Walter,
You could check a few things to see what's going wrong:
1. When outlook cannot send mails, can you ping the exchange server?
If you can't ping, then do a packet-tracer command on the ASA to determine if and why the ping packet is being dropped.
packet-tracer input tcp detailed
If the packet is dropped on the ASA, this command will tell you why.
2. Are there any connection limits configured for the exchange server. These can be configured in either the policy-map or in the static nat commands.
3. The 5505 base license has a limit on number of internal users. So if this outlook problem is only for a few users, and ASA has base license, then it could be because of limited users.
4. You can run captures on the ASA on both interfaces, to see packets to-and-from the Exchange server. If you see packet entering the ASA and leaving, but no reply coming, then it could be an issue with the server.
Hope this helps.
-Shrikant