Google calendar invite is blocked

Google calendar invite is blocked

When the some send google calendar invite to our user, it gets the bounced back. Please help.

Error Icon

Message blocked

Your message to xxxx@mydomain.com has been blocked. See technical details below for more information.

The response from the remote server was:

554 5.2.3 MailPolicy violation Error delivering to mailboxes

Reporting-MTA: dns; googlemail.com
Arrival-Date: Fri, 21 Aug 2020 00:10:08 -0700 (PDT)
X-Original-Message-ID: <00000000000056a52005ad5ded1e@google.com>

Final-Recipient: rfc822; xxxx@mydomain.com
Action: failed
Status: 5.2.3
Remote-MTA: dns; mx.zoho.com. (136.143.190.121, the server for the domain mydomain.com.)
Diagnostic-Code: smtp; 554 5.2.3 MailPolicy violation Error delivering to mailboxes
Last-Attempt-Date: Fri, 21 Aug 2020 00:10:11 -0700 (PDT)