I actually triggered an issue with this myself.
Just as an FYI to everyone...
If your rooted and you use titanium to back up your apps, don't use it to restore the mail app.
The reason: it does not add the "sync account" so it will not appear in the accounts list and it will not automatically download messages.
It works manually just fine.. so i you open the mail app it will sync immediately and if you "pull down and release" it will sync as well.
It just will not sync on it's own.
So, beware if your using titanium to restore the settings for this app.