Here is a real strange but evidently real issue for Omnia II users: if you have Exchange + McAfee Anti-Spam E-mail Toolbar working in tandem, it appears that some of your emails won't come through when using the Omnia II with WM6.5.
User UpHillBattle (indeed) writes
I'm experiencing a strange problem with my new Samsung Omnia II (WM 6.5). I have set up ActiveSync (on the cell phone) to sync e-mail, contacts, calendar and tasks with an Exchange Server. I used the same setup on my older HTC Touch Cruise (WM 6.1) and had no problems then.
The sync appears to be successful after setup, but later some e-mails are synced to the Omnia II while others are not. I have reset the device to factory settings and set up the connection again, only to experience the same thing: Success at first, then later some e-mails are received, while others are not.
Upon some diligent testing he later responds
...it's the McAfee Anti-Spam E-mail Toolbar. For those of you that don't know McAfee, it has an optional toolbar that can be enabled in various e-mail clients (Outlook 2007 in my case) and that lets you manually mark (or unmark) e-mail messages as spam. When I disable the toolbar, everything is fine - when I enable it, I get the problems described above.
Both Samsung and McAfee have been made aware of the problem and a fix of some sort is expected in the future (vague, eh?). Until then, if you have this gruesome-twosome setup, best to follow UpHillBattle's advice.