Anyway, It has been some years since I last used IMAP. I had issues with Outlook, Thunderbird and Nylas N1 while connecting to Gmail, Exchange and Office365. It was a fairly small mailbox getting about 20k mail a year and keeping about half of that. Usually moving about 5k mail around at a time (end of year).

It got so bad that I had to get familiar enough with the IMAP protocol to make my own client program to handle deduplication overnight. Shortly after that I decided to just give up on trying to keep thinks organized.

I am in Australia and this was before the NBN, so obviously it was always on shitty connections.