I had added a new imap account to my mailserver and I had bought a new phone. This phone (motorola g5s) comes pre-installed with the Outlook app made by microsoft as an email client.
As I am lazy by nature I did not want to install an extra email client, so I decided to add my imap account to the Outlook app. Checking the logs of my mailserver, I saw an incoming connection that was authenticating succesfully using my credentials. But the connection did not originate from my IP! I was using the ip address 94.xxx.xxx.xxx and the client connected from 52.xxx.xxx.xxx!
Microsoft is playing man in the middle and thus has acccess to all my mail in the imap account!
Nice one Microsoft. From now on I am only using Outlook for Microsoft mail accounts, as they have my authentication data for these already…..