Cannot Send Mail the Sender Address is Invalid on iPhone

How to solve the error “cannot send mail the sender address is invalid” on an Apple Device

Prerequisites: iPhone familiarity 

Difficulty Level: Member • Nerd • Platypus

Estimated Time: 5 minutes

Expected Outcome: You can send emails again

Tools Required: iPhone, email password

Method 1

1. Go to settings on your iPhone.
2. Under "Passwords & Accounts" look for the problematic email address.
3. Click on the account and if the options are grayed out, the email's password must be reentered
4. This will prompt you to reenter your password via an extra option present under the grayed out options.
5. The username is the email address, and then type in the password for the email address.
6. Once completed hit “Done” and try sending another email. The issue should be resolved.

Method 2

Sometimes the Apple Mail app is unhappy when it is missing some information it calls "optional". If you fill in this information, this sometimes corrects the issue of "Sender Address Invalid".

1. Go to settings on your iPhone.
2. Under "Passwords & Accounts" look for the problematic email address.
3. Click on the account
4. Select the email again at the top of the page.
5. Tap Outgoing Mail Server. Tap Primary Server.
6. Fill in all fields including optional fields
   1. Username
   2. Password
   3. Use SSL/Authentication
   4. Port #

Method 3

Sometimes the Apple Mail app is unhappy if it is missing a description for the email account. 

1. Go to settings on your iPhone.
2. Under "Passwords & Accounts" look for the problematic email address.
3. Click on the account
4. Select the email again at the top of the page.
5. Under Description, tap in the field and delete whatever is currently used.
6. Enter your full email address as the Description.