I have been corresponding with a client today. Suddenly my replies are not allowed through. I am unclear on how to resolve the issue. The error text is captured below.
INVALID_ADDRESS, ERROR_CODE :550, ERROR_CODE :Please turn on SMTP Authentication in your mail client.
sender163-mail.zoho.com [74.201.84.163]:21463 is not permitted to relay
through this server without authentication.
I am happy to change any settings,but am unclear why this suddenly stopped working today.
Thank you,
Blake