NVALID_ADDRESS, ERROR_CODE :554, ERROR_CODE :5.7.1

Emails for my forums are not getting sent, and I am getting this in my inbox:

This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error.

-emailadress- INVALID_ADDRESS, ERROR_CODE :554, ERROR_CODE :5.7.1 -emailadress-: Relay access denied

Received:from smtp.zoho.com (serverip [serverip]) by mx.zohomail.com
with SMTPS id -id-; Sun, 20 Mar 2016 06:51:10 -0700 (PDT)

I am behind cloudflare, and my email settings are set up via ipboard, using SMTP protocol SSL. When I send test emails on ipboard it says this:

The email could not be sent. Check the settings entered are correct or contact your hosting or SMTP provider for more information.

535 Authentication Failed

It used to work, then it randomly stopped. Any help is appreciated!