I have been using Outlook 2007, however I swapped over to em client as IMAP was a pain in the arse in Outlook.

Looking at returning to Outlook 2016.

Does anyone use Outlook 2016 and if so does IMAP function correctly?

Outlook is a fantastic Exchange / O365 client but an poor one for regular “Internet” mail. I’d use Live Mail or Thunderbird or something. (Though these days I use web clients exclusively.)

That said, I’m not aware of any specific problems with Outlook and IMAP.