As of now, using the 770's native Mail app is useless even with IMAP. Even when I configured an account IMAP account, it retrieves the email with no problems, the problem however lies in syncing mail with your account which doesn't happen. I tried the following:

1. Retrieved email on the 770 - worked.
2. Retrieved and deleted several email (spam) from my PC using a different client. I made sure to resync again so the server would delete the email internally.
3. Retrieved again using the 770. Supposedly, the 770 mail app should be smart enough to sync the contents since it is using IMAP, but the emails that I deleted from the PC is still on the 770.

I can conclude that the 770 mail app doesn't sync with the mail server. It just keeps on retrieving emails. This would make the internal email database bigger and bigger and slower and slower since it keeps on sorting when you click on a folder on the left side.

The mail app is not ready until they fix this issue. For the mean time, I suggest you use an online email client.