I would suggest you star5t by setting a more realistic timing on getting new mail. Like 10 minutes. If your bandwidth is limited it is unlikely any of your fetch processes actually completes before it is run over with a new one.

Thanks for your reply. It would be strange for me if setting the time to 10 minutes would fix it as I don't understand what kind of data it receives to make it by the end of the day 30GB ?! Nevertheless, it would be also non-reliable to get updates every 10 minutes, I was actually looking for push service and because I didn't find it, I used 1-minute sync instead.

I will anyway change it and see if that would make a difference.

Thanks.

Well it may just be sending the same 40 or 50 bytes over and over again. That is the point when things run over one another what happens is basically unpredictable. It might just be sending the sign in data over and over and perhaps even getting login fails because you are still logged in the the server.

If you server supports push (like Google) then it will be there automatically. In account settings under "allow immediate notifications when new messages arrive" in Server settings. Microsoft say they support idle. https://docs.microsoft.com/en-us/exchange/clients/pop3-and-imap4/pop3-and-imap4?view=exchserver-2019

So really your reluctance to set a reasonable time based check has no basis. Be assured 1 minute is unlikely to actually effectively complete a single fetch. Unless it is to fetch nothing perhaps. That is the sort of time frame you might select to use if you had the exchange server also sitting on the same desk as your device that they were connected with a fibre cable. There are a lot of people coming to these forums with all sorts of odd issues with their email created by inappropriate fetch frequencies. It may not be your issue. But I strongly feel it is at least part of the problem.