How I Fixed an iPhone that Couldn’t Get Mail Unless On WiFi

Updated October 3rd, 2020.

Does your iPhone get mail when it’s on WiFi, but not when it’s on Cellular? Here’s a fix for that problem. Hint: It has to do with the iPhone’s Cellular Data settings.

Executive Summary

Settings > Cellular > Cellular Data should be ONScroll down… Mail should be ON

(Thanks, John, for the “Executive Summary” idea.)


The Problem: Mail worked on WiFi, but not on cellular data

My friend Laura dropped her iPhone 6 and cracked the screen. She was going to get a new one, but decided to get the screen replaced and keep using it. Everything seemed fine after the repair.

But Then…

Laura called me (I’m her iPhone and Mac consultant) to say that her email wasn’t working on her iPhone. She kept getting messages like this one:

iOS 10 Cannot Send Mail message (because iPhone is not on WiFi)
Cannot Send Mail

I had her check the settings for Mail and they seemed fine. I tried setting up one of my spare iPhones with Laura’s email settings and I was able to send and receive from both of her accounts– obviously, if I could sign into her accounts, we knew the right settings. And since I was able to send and receive emails from both of her accounts, her email accounts were working fine.

I asked Laura to try sending me an email and to our surprise, it worked. She also received my reply. Problem over, or so we thought.

The next day, I got another call from Laura. “It’s not working,” she said. This time, I asked her where she was. “Florida,” she said (I was in California so I couldn’t fix her iPhone in person). She was on her way to a meeting. In the car. The funny things was, we both knew Mail worked perfectly yesterday.

I asked Laura, “Where were you yesterday, when your iPhone’s Mail worked?”

“In my hotel,” she said. “On their WiFi.” “Aha,” I thought. “Mail works over WiFi, but not on Verizon’s network. Something must be wrong with Cellular Data.” Maybe it was turned off. Laura checked (Settings/Cellular)– it was on.

Cellular Data in iOS-- ON
Cellular Data in iOS– ON

My next guess was that maybe there was something wrong with Laura’s account with Verizon. Maybe she was over her data limit. Laura checked into it– no problem.


A Brilliant Idea (that didn’t work)

Then I had a flash of inspiration. “Try going to web pages with Safari,” I said. My guess was that this would not work and that we would narrow our problem down to something wrong with the network connection (or maybe the antenna) when not on WiFi. But guess what? Safari worked just fine over cellular, in the car.

To recap: when on WiFi, Safari worked, and so did Mail. When on cellular, Safari worked, but Mail did not. We knew we had the right settings for Mail because the accounts worked fine when on WiFi. And we knew the cellular data antenna worked, because we could use Safari and load web pages when not on WiFi.

It wasn’t the phone itself

Laura went to a nearby Apple Store, told them her story, and they sold her a nice new iPhone 7, hoping it would solve her problem. She left the iPhone 7 in the box for me to set up upon her return to Los Angeles.

At this point, the old iPhone still didn’t work right. Actually, the only thing it had trouble with was Mail– the iPhone would not send nor receive email unless the iPhone was on WiFi. Everything else worked fine– Messages, phone calls, Weather, other apps.

The old iPhone was backed up to iCloud, so I set up the new one by restoring that backup to it. Restoring a backup to a new iPhone can be a very lengthy process, as this one was, but I had to wait it out to see if the new phone could get mail when not on WiFi. When the new iPhone was ready I tested sending and receiving email over WiFi, and it worked perfectly (as expected). Then I turned WiFi off and tried doing it over cellular– and it did NOT work.

Now I knew we had a software (or settings) problem, because the new iPhone (a clone of the old one, software-wise) had the exact symptom exhibited by the old iPhone. In effect I’d copied the problem to the new iPhone.


The Fix for the iPhone that wouldn’t get Mail over cellular

I looked at Cellular again. Yes, it was on. But this time, I scrolled down. This revealed a section of Cellular’s settings that I hadn’t looked at. It’s called “Use Cellular Data For:” and here’s how it looked (this is iOS 10– other versions may look a little different).

iOS Settings Use Cellular Data For
iOS Settings Use Cellular Data For

Scrolling down a little more I saw this:

Cellular Data OFF for Mail
Cellular Data OFF for Mail

I was very, very surprised to find that “Use Cellular Data For” was turned OFF for Mail! So many apps were allowed, but not Mail. Naturally I flipped the switch for Mail to “On” and the problem went away.

Note: if, for some reason, you turn “Use Cellular Data For” to OFF for Mail, you’ll get a big warning telling you your mail won’t work right if you do that. Apparently, with Laura’s iPhone, the warning was not shown, or not seen, or not understood– certainly not remembered.

UPDATE: in iOS 13, Mail’s settings include the Use Cellular Data switch. If you turn it on here, it turns it on in the “Cellular Data/Use Cellular Data For” section. One setting, in two places. Looks like this:

Mail settings in iOS 13, with Cellular Data on (yours should be on too!)
Mail settings in iOS 13, with Cellular Data on (yours should be on too!)

Summing it up

As usual, solving this problem started with figuring out what the problem was. We started out thinking the problem involved the iPhone settings for Laura’s email accounts, but that wasn’t it. Then we thought cellular data might be off– but we saw it was on. Then we thought it might be something wrong with the cellular antenna, but we were able to use Safari over cellular, so that wasn’t it either. Then we thought there might be something wrong with Laura’s account with the cellular carrier– but that wasn’t it (Verizon said so, and again we knew we could use Safari, and that uses the same cellular data as the Mail app).

Finally, having looked at the master switch for Cellular data a second time, we had the idea of scrolling down (on a Settings page that doesn’t look as if it has anything to scroll). I think it was just bad luck that the Cellular settings screen fit so perfectly on the iPhone 7– had it been cut off in the middle or something, we probably would have realized that there were more settings below and that we should scroll down to see them. Anyhow, once we saw the “Use Cellular Data For:” section, we zeroed in on the problem, and fixed it right away.

Sliding the switch to let Mail use cellular data was easy. The hard part was figuring out what the problem actually was. Sometimes it’s the other way around– easy problem to figure out, hard problem to correct. Here’s a story about a wrestling match I had with an iMac a few weeks ago (I won).

Bonus: here’s how to forward a voicemail message received on your iPhone.

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