Can't use email unless connected to wifi

[Stonetica]

Not sure whether the problem is with the device (settings), the app (yahoo email and gmail), or the service (Verizon). Both email accounts, and both apps, work fine when connected to my wifi. Neither works when NOT connected to wifi. By that, I mean I can't send or receive email.

Also, when I drive in my garage and automatically connect to wifi, several notifications show up for multiple apps, but I'd hate to say which ones at this point, because I'm not sure.

Right now, I've turned the wifi connection off. My status bar shows 4GLTE.
Under Settings/Data usage: mobile data is ON; Set mobile data limit is not checked.
I can access web pages, facebook, etc.

In the yahoo mail app, enable notifications is on, for all emails.

I have an email in my outbox that I tried to send while not connected to wifi. If I wait long enough, I'll get a notification about an error related to this email.

I've tried going to settings/accounts and syncing my yahoo mail accout (which is actually at sbcglobal.net) but the email won't send.

Any ideas? Surely I SHOULD be able to email while out on the town?

 

[Stonetica]

OK. Well nevermind, sort of. I've been running tests by changing the "preferred network type". It is now back to the original setting (Global), but the status bar says 3G, not 4G, and email is working. Now I'm curious why it might have changed if you have any input on that, but at any rate, my email works now without being on wifi.