In order to prevent emails from getting deferred, follow the below steps on configuring non-throttled hosts within ProofPoint.
Log in to the ProofPoint administrative console
Select Email Firewall > SMTP Rate Control > Non-throttled hosts
Select Add
Add our delivery server IP addresses:
159.183.82.50
Click save
If emails have already been deferred due to a preexisting policy, follow the below steps.
Log in to the ProofPoint administrative console
Select Email Firewall > SMTP Rate Control > Connections
Search for the Nectar Comms IP Address: 159.183.82.50
Add Hostname and IP address to Non-Throttled Hosts
Note - Proofpoint may have multiple servers (seen in the top middle of the page) that rules need to be applied against.