Apple Mail Cannot Send Emails

SMTP Send Problems with Apple Mail

If you are having problems with Apple Mail SMTP using IMAP, ensure you are using the following settings:

Mail > Preferences > SMTP > Edit SMTP Server List > Advanced

Automatically detect and maintain account settings: No
Port: 587
Use SSL: No
Authentication: MD5 Challenge-Response
Allow insecure authentication: Yes

For more information: How to setup Apple Mail