For the last two weeks or so I have had a weird issue with Mail. It tells me it's unable to connect to either of my email accounts (verizon and gmail) and takes both offline.
For a while restarting the MacBook seemed to fix this some of the time. I have gone through and rechecked all the passwords, etc. and I can get at my mail accounts through Safari using the verizon.net and gmail.com browser interfaces.
The verizon account is POP and gmail is IMAP, so it's apparently not related to the mail protocol.
This has gone from merely annoying to a serious problem.
MBP 2.26G Core 2 Duo, 8GB RAM, Mac OS X (10.6.5), Mail 4.4 (1082)
Your Mail accounts are looking to their original connections to find the email servers that you setup. When the VPN is running it cuts off the connection to those original servers in favor of the servers in the VPN network.