I have recently started using Thunderbird 52.0.1. I use Thunderbird for two accounts, both Outlook, one through my school's 365 and one just outlook.com. The school account works well, the outlook.com account does not. I repeatedly get error messages as indicated in the attached screenshot. Things I have tried: creating exclusions for my profiles (no effect); starting in Thunderbird safe mode (no change); using with or without my VPN (expressvpn) on (no change); repairing inbox.msf file (no improvement); compacting folder (no effect); changing the size of the cache (no effect); decreasing the size of INBOX file that is kept locally (no change); re-entering my password as I am sometimes prompted to do (no change); changing how often mail is checked, anywhere from 1 minute to ten minutes (no effect). I am running outlook imap (imap-mail.outlook.com; port 993; SSL/TLS; normal password). It does occasionally work, but for seemingly no reason. I'm not a computer person so I don't doubt that I'm missing something, I'm just trying my best.