I see FengOffice relies on email for messaging among users. This is not quite good solution as email is used for much more stuff than monitoring collaboration.
My coleagues use email for lots of stuff and also use email clients to get email. They cannot leave email on POP3 server so FengOffice could catch it too. Simply said, they refuse requirement to let FengOffice handle their email.
It is also not good to have separate email just for FengOffice usage, as that removes the most important role of email - to be notified that something new happened and that you have to log in to the FengOffice to check it out.
Email usage with collab software can be useful for notifications but not as messaging system. It would be better of FengOffice offers it's own internal messaging system, and use mail just for notifications, as, probably, most of the people expect.