I figured this out on my own.
Apparently the most recent iOS update changed all previous SMTP settings to MD5 Challenge-Response. The resolution is as follows:
- From the home screen on your device tap Settings, and then Mail, Contacts, Calendars.
- Then tap the email account under Accounts.
- Tap Account.
- Scroll down and tap SMTP under Outgoing Mail Server.
- Tap on your Primary SMTP server.
- Tap Authentication.
- Change MD5 Challenge-Response to Password.
- Tap the button on the top left to go to the previous screen, then click Done.