Somewhat related, I recently realized that Microsoft Outlook on Android fetches _all mail_ on Microsoft servers, then sends it over to the app. If this is menti

Somewhat related, I recently realized that Microsoft Outlook on Android fetches _all mail_ on Microsoft servers, then sends it over to the app. If this is mentioned anywhere when setting up the account, I totally missed it. This led me to look for a "pure" email client that would _only_ contact my server. Popular apps like Blue Mail and myMail did not work at all behind a firewall that blocked random internet access. I am happy to report that K-9 mail (open source) was what I was looking for: it never tried to access anything other than my mail server. I wholeheartedly recommend using NoRoot firewall (or similar) to see just how many random servers your (flashlight) apps talk to (and watch them fail miserably when you block that).