IMAP Path Prefix icloud mail issue

Had some issues with iCloud mail being slow. Turns out (after a couple of days) that my internet was having troubles and not iCloud. Talked to a friend who advised me to enter the IMAP Path Prefix in Mail for the iCloud account. (did: imap.mail.me.com)

After that on iCloud there was a new folder created with the name imap.mail.me.com and in that folder another one for Sent Messages in which the sent messages synced from my Mail application on my macbook pro showed up. But no longer in the normal Sent folder (the one with the paper airplane).

Talked to my friend again who told me it should have been p99-imap.mail.me.com so I keyed that in.

After that on iCloud there was another folder (you can guess) p99-imap.mail.me.com with a subfolder imap.mail.me.com and another subfolder in there called Sent Messages which now is used to sync the sent messages from my Mail application on my macbook pro.

In the Mail application the normal Sent folder (paper airplane) for my iCloud account only showes the recently sent items that were synced with the Sent Messages folder in iCloud.

In the Mail application under my account name I now have a Sent Messages folder with all old synced messages, prior to all these changes.

What to do???