We have 6 users on our domain for email. We use it for low frequency emails and its also used in a CRM (Insightly). But we don't do any bulk emails using it, any emails beyond 50 people at a time get exported to a newsletter program.
So several users seem to be having email receiving and delivery problems. We sent a test email to one of the users and got this bounce back -
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain sanfranciscobookreview.com by mx.zoho.com. [74.201.155.125].
The error that the other server returned was:
554 5.2.3 MailPolicy violation Error delivering to mailboxes
Can you please troubleshoot and fix. Not having reliable email isn't good.