do you use anti virus? How large is your send folder? Is the Sent in an IMAP aor a POP mail account?

The problem seems to have resolved on it's own, at least for now :)

I have 5 active POP email accounts. The sent folders vary in size from 1.5MB-2.5GB

I would suggest trimming down those large folders. We often see issues with large folders and the actively updates frequently. For instance the 2.5Gb file that holds that folder probably has to be scanned by your anti virus multiple times a day as you send new mail on that account. Moving most of the mail to another archive folder and only updating a much smaller folder reduces the load on your system and hence is often likely to improve performance.