We have enabled SMTP authentication to prevent spammers from using the SMTP (outgoing) server as an open-relay allowing them to freely send any content they desired. We have implemented the feature to prevent the mail server from being blacklisted by other mail servers running anti-spam services which would reject all emails from the server if we were found to be a spammer-friendly haven. This is not acceptable and would impact the service for legitimate users.
To overcome this we had to enable a feature called SMTP Authentication.This basically means that every time an email is sent by the server it asks for the username and password to verify if the user is legitimate. The solution is to enable SMTP-Authentication in your email client.
If this is not enabled on your email client (outlook, thunderbird, etc) you may see the following error:
"error 553, that domain isn't in my list of allowed rcpthosts (#5.7.1)"
Please review our video tutorials at the below link on how to correctly setup your email account to work with our mail servers.