POP3 to IMAP email configuration: how to do it step by step?
Please see the following:
First of all, we’d recommend making a backup (Menu -> File -> Backup)
Afterwards, set the account again in eM Client as IMAP (you now have your account twice in eM Client)
See if setting the account up as IMAP makes the content of your mailbox synchronize.
If it doesn’t, you can try moving your messages from your POP account to your IMAP account. We do however have to warn you that sometimes, when a lot of messages are transferred onto the server, it can cause errors. If you however have a backup, you have something to Restore from (through Menu -> File ->Restore).
When you have your data transferred, you can delete the POP account through Menu ->Tools -> Accounts