Microsoft 365 Outbound Email Relaypool

This post is an update about the configuration of email relaying or forwarding via Office 365. A recent enhancement in April 2022 is now being followed up with an additional update to further improve the security and reliability of email services. Effective May 30, 2023, special relay pools used for relayed messages via connectors will be updated. This update will only affect messages sent from domains that are not registered as accepted domains in the tenant. To avoid service disruptions, the post suggests completing the suggested actions outlined below.

When this change is implemented, outbound emails sent via connectors will also use the relay pool if messages do not meet any of the below criteria. The affected messages may end up in the junk folder of the recipients. Therefore, you need to make sure you review and complete the recommended actions listed below to avoid any service disruptions:

• Messages will automatically bypass the relay pool for outbound sender domains that are an accepted domain of the tenant.
• Passing of SPF when the message reaches Microsoft 365.
• Passing of DKIM on the sender domain when the message arrives at Microsoft 365.

In cases where incoming email does not pass SPF for relayed messages, the Sender Rewriting Scheme (SRS) rewrite will be skipped. Once the change takes effect, you can identify messages sent via the relay pool by checking the outbound server IP in the message header from the recipient's end. An outbound server name with "rly" in the name indicates that the message was sent via the relay pool. To ensure that messages go through the regular pool, make sure that the sender domain of the outbound message matches an accepted domain of your tenant, SPF or DKIM. To enable DKIM for the sending domain, you should ensure that DKIM is enabled for the specific domain.

The post Microsoft 365 Outbound Email Relaypool originally appeared on M365 Admin.