iOS - Mail auto-fetch will not disable

Question

Since iOS 13 Mail seems to auto-fetch new mail every time the iPhone is plugged into any charging source, either Mac or simple wall-wart.
Late Edit: This has continued through to iOS 14 & 15, even on new iPhones.

I've always had my iPhone set to manual Mail fetching for all except my actual Apple iCloud account, which is my only IMAP account & only used for official notifications from Apple.

My main email is done over a POP3 structure, intentionally so I don't have a phone-full of emails. These have always been set to only fetch if I launch the Mail app.

I've always had the main Push* setting on, but then setting each individual account except iCloud to Manual. Switching off this main Push seems to have no effect.
*Settings > Passwords & Accounts > Fetch New Data > Push

This has affected every iOS from 13.0 & continues in 15.1

Edit May 2020 - no fix but a rapid workaround -
iOS iPhone/iPad Mail - rapid mass delete/delete all

Answer 1

After several weeks of testing - this doesn't work. All it does is prevent the badges, not the actual unwanted mail fetch

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What appears to fix this is to turn off Notifications for Mail

Settings > Notifications > Mail > Allow Notifications.

This does mean that you never see Badges if/when any mail at all is received, so you do have to actually launch Mail to see if it worked… which then loads manually, of course.

Answer 2

Sounds like a bug. Wife’s phone will check every night when she plugs it in before bed. Started with iOS 13. She’s uses imap account with manual fetch enabled.

Answer 3

If you have push notifications turned off and fetch set to automatically it displays the statement that new data will be fetched in the background only when on power and Wi-Fi. If manually, hourly, every 30, or every 15 minutes is selected, this statement is not shown. Sounds like no matter what is selected it remains in automatic mode.