Interesting one this.
When I allow a user to see the MD's Exchange mail box (cirxca 12GB) she starts to get the error message:
"There is not enough free memory to run this program. Quit one or more programs, and then try again."
What is odd is that F9/Send+Receive and auto e-mail updates no longer work and you have to manually press the Update option to receive mail.
The machine has 4GB memory of which 2.5GB is free. The same phenomenon happens in "outlook.exe/safe" mode.
I have tried this on two machines and when you add in the second Mailbox this problem begins.