Problem with synching AOL Sent mail and my Apple Mail

I'm running Mail 4.5 on a MacBook Pro: my mail provider is AOL. I've noticed recently that the AOL Sent folder is out of sync with my Apple Mail Sent: there's lots of missing messages from the AOL Sent file compared with the Apple Mail. I've tried rebuilding the Sent folder: there were a couple of messages that it got stuck on which I had to delete, and then the process completed: but after the rebuild I've still got the out of sync problem.

I'm sending and receiving messages ok: the Inboxes are in sync. But the fact the AOL Sent folder is out of sync is concerning.

Has anybody any suggestions on where to look next? Many thanks

 

Thanks for the response. Yes, AOL uses IMAP and I'd already checked the settings: so the flag is set for storing 'sent' messages on the server. It has stored some on the server but there are gaps where it hasn't: the reason for that is not apparent. So I'm trying to (1) get the folders back in sync, and (2) find out what's wrong so I can stop it happening again. (The rest of the folders - inbox etc. - are fine and in sync). Any advice appreciated.