Q: Software Update

User troubleshooting on the iPhone consists of restart, reset, restore to backup, restore to factory.

Restart your iPhone, iPad, or iPod touch - Apple Support

Restore your device from an iCloud or iTunes backup - Apple Support

Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support

I have several devices using iOS 9.3.2, and have experienced no problems whatsoever. I also consider myself a heavier user, including an Exchange account, and also having the Apple Watch paired to my device.

restart Restart your iPhone, iPad, or iPod touch - Apple Support

Restarting is only the first possible troubleshooting step. If that didn't help, time to move on to the next step.

Please review ChrisJ4203's post above. He outlined the next steps and provided helpful links.

User troubleshooting steps in order, as I indicated in my earlier post are restart, reset, restore from backup, restore to factory, testing after each step. I provided a link with the steps to perform each of the steps indicated.

If mail crashing is your only problem, you may also want to try removing the account and adding it back. Many times as we use our devices over and over, files and data can become corrupted. This does not always become apparent until we do something major like an iOS update. This will identify these issues and it is necessary to troubleshoot, and many times restore the device to factory to overcome the corrupt files. Good luck.