This KB article assumes that an organisation account has been created in Proofpoint Essentials, and a privileged user account exists and is being used to manage this organisation. If you have a question related to POP or IMAP, please see the knowledge base article about that. The steps to start processing inbound email are as follows:

1. While logged into the user interface, navigate to Company Settings > Domains tab
2. Click New Domain button
3. Enter the domain name
4. Choose Domain purpose.  Management is for solely managing the domain.  This setting will not relay email.
   1. If domain purpose is Management than proceed to step 8.
   2. If domain purpose is Relay than proceed to step 5.
5. Enter the Primary SMTP Destination IP Address or hostname where we are sending your mail to. Make sure the SMTP destination can receive email via port 25 and accept email for your registered domain.
6. Add SMTP Failover 1, 2, 3, 4 IP addresses (Optional)
7. Ensure "Enable email relay?" option is set to "Yes". 
   
8. Click Save

Important Note: Remember that changes here take place every half hour. (Top and bottom of the hour)

Additional Information:  These steps are also located in the Getting Started Guide

Please refer to the following knowledge base article for the recommended procedure to updating the MX records: [Setup Step 2]