IPhone :: Mail Comes Down But Not Up After Upgrade To IOS 5.1

I use iPhone Mail to sync with my mail server. (I also use Mac mail on my iMac to sync with the same server.) Everything's been fine until I upgraded to iOS 5.1. Doesn't look like anyone else is having the same issue, so maybe it is a setting?

Anyway, the mail comes down to the iPhone, but strangely, there's no little red number on the Mail home screen app anymore. When I go to the list of mailboxes, INbox also doesn't have the new messages number anymore. When I physically go into INbox, the new messages appear and I can read them. If I read them, the next time I check my mail they come down as new again. I can delete messages locally, but upon syncing, deleted messages come down again as new (I presume the server is not getting the message). Sent messages don't show up on the server (and they sound like they're going out, and no errors pop up), yet I have no record of them anywhere. Drafts don't show up on the server.

When I go into Mail on the iMac, all mail comes in as if the iPhone never got the messages. Until day before yesterday, read messages from iPhone would be read in the iMac inbox and syncing worked great between all three -- iPhone, iMac and server.

Info:iPhone 4S, iOS 5.1