A client of mine has been receiving bounced emails with the following message:

Received <<< 554 denied by gorbs

Here's the fix:

The recipient who is unable to receive email from you due to the Gorbs messages, must email support@verio-hosting.com and provide their domain name, include the bounced email and a message similar to:

Please remove the block against the mail server at 'sending-mail-server-ip-address'. We need to receive email from this mail server."