If Proofpoint Essentials users are unable to receive email from certain email addresses, it is most likely an issue with the sending mail server. However there are a few possible areas where this may be a configuration issue on the Proofpoint Essentials platform:

1. There may be a rule in the ‘Filters’ section quarantining emails from that address or domain.
   
   To view Company filters:
   1. Log in to the Proofpoint Essentials user interface
   2. Type the customer name into the search bar (top header)
   3. Click on Company Settings
   4. Click on Filters
   
   
2. There is a 3rd party MX Record pushing some email towards another mail server.
   
   
3. The sending server IPs may be blacklisted. We mainly utilize Proofpoint Dynamic Reputation (PDR) service for connection level validation, but also take in other feeds along with PDR. You can verify if an IP is being blocked by PDR here: http://www.proofpoint.com/support/ip-lookups.php.

If further assistance is required, please contact support with as much details as possible i.e.

• Non Delivery Report (NDR)
• Sending Server IP address
• Sender's email address
• Time and date the email was sent
• Also note that if an email is bounced the bounce error will also provide details as to why it was bounced which may help identify the cause