I too had this problem - mail notifications not showing on my Lock Screen.
I checked every single setting that others here and also other sites have suggested and mine were already set that way.
*My solution, my notifications had been working but then suddenly stopped.
I finally realize what it was (and hope this works for everyone else), settings>notifications>mail>”make sure Banner Style is set to Persistent!”
As you can see it in my screenshot below.
I had become “annoyed” having them show up as “Persistent Banners” across the top of “any screen” I was using (and interrupting me while playing a game,etc.) - so at first I “changed the Banner Style to “Temporary”, and then finally “Deselected Banners” altogether while leaving the Lock Screen still checked.
”THAT was the cause of the problem”. It seems that if you want a Mail Notification to appear on the Lock Screen and stay there, you’re stuck with selecting a “Persistent Banner” style, and that choice of “Persistent” only appears if you “Select Banners”.
* The only other glitch might be me, I’m using GMail, and for some reason “Gmail” does not give the “Push” option, only “Fetch” (apparently a GMail thing from what I’ve Googled on it). Go to: Settings>Mail>Accounts>then tap on “Fetch New Data” - mine was set to “Push!”, but when I tapped on that, “Push” was selected only for “iCloud”, tapping on GMail only gave the options to “Fetch” or “Manual” (see second screenshot)
Other mail programs like Outlook do give the “Push” option when you navigate that way - so the issue may be a combination of settings when you use GMail like me.
I hope this very long answer helps someone.
