I had the same problem after trying to download an xls file.
I tried stopping SyncManager as well as com.android.email, and no luck.
I think it might have been "stuck" trying to read the file. (Ugh... terrible implementation of email.)
At any rate, I found a workaround.
Go to Home>Settings>Applications>Manage Applications
Click the Menu button and select "Filter"
Scroll down to the "Email" application. Select "Clear Data"
(This is effectively the same thing as deleting the account and starting over, however when I tried to delete/recreate the account using the UI, it didn't work. After deleting the information through the Application Manager, it appears that my email is working now.)
I reconfigured it without SSL, to only show one day's worth of email, and to scan every 5 minutes.... so that it doesn't saturate the system resources.
Hope this helps.