Updating Password Authentication Method on Mac Mail
To ensure Mac Mails's settings are properly configured:
1. In Mac Mail, go to "Mail" > "Preferences..."
2. Select the Accounts tab. Under Account Information, click the drop-down next to Outgoing Mail Server and select "Edit SMTP Server List..."
3. Select the Advanced tab.
4. Under the Authentication drop-down, ensure Password is selected rather than MD5 Challenge-Response.
5. Click OK to close the SMTP window, then OK again to close Preferences.