Recently we've switched to different hosting provider and cannot get Zoho mail to work. We can receive emails but cannot send, getting this type of message:

"Unable to send message. Reason: error 533 Relaying disallowed. Invalid domain - administrator@supersecretservice[dot]pl"

My research points to MX settings but they seem to be correct.

Domain: supersecretservice[dot]pl

Any help will be appreciated!

Regards

Paul