help @ work, mail server not allowing from outside company

boss is gone for the week, if anyone has any input greatly appreciated.

we're running an exchange email server, which i have access to.

mail is flowing locally in the company but nothing is being received from the outside. It can be sent out, but when I attempt to send something in, im getting:

PERM_FAILURE: Gmail tried to deliver your message, but it was rejected by the recipient domain. The error that the other server returned was: 550 550 5.1.1 <XXXXXXXXXXXXXXXXXXXXXX>: Recipient address rejected: User unknown in relay recipient table. We recommend contacting the other email provider for further information about the cause of this error. Thanks for your continued support. (state 14)

I think it's a problem with our mail filter servers.. how can i find these?

Your relay is not allowing passage because the user account is not authenticating. The account is either incorrect or missing.

thanks for trying but i got it figured out.

for some reason the mail backups were extremely large, and filling up one of the drives on the server, causing the mail to be held in the filter before going to the mail server.