Engelmann. im trying vpn too
I dont know If you can control that, but pop and imap server have a pannel in "other email settings" of e-smith manager, and imp webmail can use the smtp server.... so I'm thinking we could check the number of pptp simultaneous connections. also in the manager (remote access)
If you are using a client e-mail software in your vpn client machine , maybe it needs an aditional connection.
Alejandro