Email Security.cloud Action Required: Relaying Email from the Microsoft High Risk Delivery Pool (HRDP)

As part of our ongoing efforts to strengthen security and protect against email spoofing, we will be enforcing stricter controls on relaying messages that originate from the Microsoft High Risk Delivery Pool (HRDP) for customers using Microsoft 365 Exchange Online. Microsoft created the High-Risk Delivery Pool, utilizing a separate IP address pool for outbound email, which is used exclusively to send low-quality messages, as outlined by Microsoft. Accepting emails from this pool increases the risk of our service being added to IP blocklists.

On July 22, 2025 we will begin disallowing traffic from the Microsoft High-Risk Delivery Pool by default for customers who use Microsoft 365.

Action Required

Therefore, if you would like to continue allowing traffic from the HRDP, you will need to explicitly designate the Microsoft High-Risk Delivery Pool as an allowed delivery option within your email security cloud management portal before the specified date.

Please refer to the Relaying Email from the Microsoft High Risk Delivery Pool Article for complete details and steps on permitting email from the HRDP.