Relaying disallowed when using Thunderbird?

Relaying disallowed when using Thunderbird?

I am attempting to use SMTP to send emails from my thunderbird client.

I initially was having problems with Thunderbird passing through my Zoho two-factor authentication, but that seems to be resolved.

I'm pulling new mail via IMAP just fine.

But when i attempt to respond i get an error

"An error occurred while sending mail. The mail server responded:  Relaying disallowed. Please check the message and try again."

Can anyone assist?  It seems authentication is working now and i am no longer getting auth errors.