Before cutting your mail flow over to Proofpoint, double-check the following:
- Under Account Management > Features in Proofpoint, the "Enable Outbound Relaying" box should be checked
- In your DNS zone, verify that each of your active domains contains the entry for Proofpoint in their SPF record
- The inbound and outbound connectors in the O365 Exchange Admin Center should be turned on
To make the switch, update each domain's MX records to the following two records depending on your region:
US Customers
Type: MX
Host/name: @
Value: mx1-us1.ppe-hosted.com
Priority: 0
Type: MX
Host/name: @
Value: mx2-us1.ppe-hosted.com
Priority: 1
EU Customers
Type: MX
Host/name: @
Value: mx1-eu1.ppe-hosted.com
Priority: 0
Type: MX
Host/name: @
Value: mx2-eu1.ppe-hosted.com
Priority: 1
One these new MX records are published, the old MX record for Microsoft will no longer need to be published in the DNS zone. Proofpoint will relay any inbound mail to this same destination after it has been filtered.