Please assist us!

Please assist us!

I have a new Zoho business account (el7araj.com). I have verified the domain within zoho control panel. When I send an meeting invitation from an external email client to to one of our customers, the email could not be delivered and I get an error saying "553 Relaying Disallowed".

Kindly do the necessary at the earliest.

Thanks & Regards,
Khalid