desktop mail will not open

Greetings Joshua, 

Based on your post, when using the Apple Mail app on your iPhone you encounter an error that the app has quit unexpectedly. 

Please check out the following article for steps to take: If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open That article recommends checking for app updates but the Mail app on iOS updates through the iOS updates. You can verify all iOS updates are installed in Settings > General > Software Updates. If any are available, be sure to have a backup prior to installing. How to back up your iPhone, iPad, and iPod touch

Let us know what happens. 

Joshua, 

Thanks for letting us know the situation has been taken care of. We're glad to hear of your success.

Cheers.