Configuring preferences and options in Outlook.com
Mike,
Thanks for the info. I don’t know either where or how to check the IMAP logs. Where is the “app-internal folder”?
I have been doing more Google digging on this problem. It seems to have been a problem for years. Many people describe the symptoms that I (and you) have. They notice it when they get a large data mobile usage invoice even though they have been using WiFi.
This entry from Jan 2018
I just got a notice from my carrier that I've use 10.5G of mobile data, so I did some digging. All of the data usage was "background" data from Outlook. To make it stranger, it all happened within 1 hr, in the middle of the night, while I was at home connected to my wifi. What gives?? My Outlook account is for work only, so I can't figure out if this is an error on my phone, or something the corporate server may have triggered.
The MS response is just to turn off background data, mobile data usage and syncing. Not very useful and not solving the problem. If, as it seems, Outlook is doing some strange things in the night I do not believe it can be anything to do with IMAP logs.
I have just installed MyDataManager app – it may help keep track of what’s happening.