I have Apple Mail set up on my mobile devices to only retrieve mail manually.
- Settings–>Mail–>Accounts–Fetch New Data–>Off
This behaves correctly on my iPhone SE (2016). It does not behave correctly on my iPad Mini 5. Both devices are running IOS 14.8.1, have SIM cards, and are connected to WiFi.
As a test, I shut down the iPad – restarted the device – and did not open the Mail app at all.
For the first two days all was fine – no new emails. On the third day there were new emails as indicated by the badge on the icon. I have repeated the above test a couple of times and after a few days it retrieves mail. As part of this test I do not open the app after a restart so why is Mail retrieving email?