550-Please turn on SMTP Authentication in your mail client

Symptoms

You receive the following error when sending or receiving mail:

550-Please turn on SMTP Authentication in your mail client

Solution

You can consult the following resources for more information on troubleshooting this issue:

Troubleshooting '550 please turn on smtp authentication in your mail client'

New or transferred account unable to receive mail: Rejected relay attempt | 550 Please turn on SMTP Authentication | $HOST is not permitted to relay through this server without authentication