Hi.

Sorry if duplicated topic, just didn't find the answer in the existed ones.

Trying to make email forwarding from zoho account to the external email.

Walked through all the steps including external email verification ( https://www.zoho.com/mail/help/email-forwarding.html).

Now trying to test forward by sending email to the zoho account but getting back the 

mailer-daemon@mail.zoho.com message with the following text:
"The following message could not be forwarded to {external email here}  for {zoho email here}

Technical details of the failure: 

SMTP authentication is required. "

Why so?