iOS 11 mail - manual fetch gone?
I also use POP rather than IMAP and also for the same reasons, although my overall setup is a little different. That said, you should be able to still manually fetch your emails on iOS 11 as follows:


Open Settings
Tap on Accounts &amp; Passwords 
Tap on Fetch New Data
Ensure that the Push toggle at top is off
Now at the bottom of the page, tap on Manually