I use imap on multiple multiple accounts on our own domain. They all seemed to work fine when only accessed through outlook 365 but since accessing some of the accounts through gmail, we have had issues with one of the accounts sychronising properly. All emails remain visible when accessed through gmail, but when in outlook 365 accessing as imap, new emails will usually appear briefly. No old emails are visible even though they still exist on the server and can be seen in gmail devices. Usually the email in outlook can no longer be seen after looking at another account or changing folders. Outlook account has been deleted and recreated with no change. Also a new install of outlook 365 on a new PC has the same problem. I can see no difference between the setups of our different accounts. Some give us full access in outlook 365 whilst one in particular remains a problem.