Skip to Content

MC266466: New outbound relay pool

We’re making some changes to harden the configuration for relaying or forwarding emails through Office 365. Starting July 27, 2021, we are updating special relay pools, a separate IP address pool that is used for relayed or forwarded emails that are sent from domains that are not a part of accepted domains in your tenant. Only messages that are sent from domains that are not accepted domains in your tenant are impacted by this change.

MC266466: New outbound relay pool

Affected Workloads

  • Exchange Online

How this will affect your organization

When this change is implemented, messages that do not meet the below criteria will route through the Relay Pool and the messages might potentially end up in the recipient junk folder.

  • Outbound sender domain is an accepted domain of the tenant.
  • SPF passes when the message comes to M365.
  • DKIM on the sender domain passes when the message comes to M365.

All messages that meet the above criteria will not be relayed through the Relay Pool. For relayed messages, we will skip SRS (Sender Rewriting Scheme) rewrite.

What you can do to prepare

When this change takes effect, you can tell a message was sent via the Relay Pool by looking at the outbound server IP (all Relay Pool IPs will be in the range), or by looking at the outbound server name (will have “rly” in the name).

For the messages to go through the regular pool you will need to make sure when a message arrives to Microsoft Office 365, SPF or DKIM passes, or the sender domain of the outbound message matches an accepted domain of your tenant

For DKIM to work, make sure you enable DKIM for sending domains for example is part of accepted domains, if the sending address is sen[email protected], the DKIM needs to be enabled for

Learn more

Message ID: MC266466
Published: 02 July 2021
Updated: 02 July 2021

Alex Lim is a certified IT Technical Support Architect with over 15 years of experience in designing, implementing, and troubleshooting complex IT systems and networks. He has worked for leading IT companies, such as Microsoft, IBM, and Cisco, providing technical support and solutions to clients across various industries and sectors. Alex has a bachelor’s degree in computer science from the National University of Singapore and a master’s degree in information security from the Massachusetts Institute of Technology. He is also the author of several best-selling books on IT technical support, such as The IT Technical Support Handbook and Troubleshooting IT Systems and Networks. Alex lives in Bandar, Johore, Malaysia with his wife and two chilrdren. You can reach him at [email protected] or follow him on Website | Twitter | Facebook

    Ads Blocker Image Powered by Code Help Pro

    Your Support Matters...

    We run an independent site that is committed to delivering valuable content, but it comes with its challenges. Many of our readers use ad blockers, causing our advertising revenue to decline. Unlike some websites, we have not implemented paywalls to restrict access. Your support can make a significant difference. If you find this website useful and choose to support us, it would greatly secure our future. We appreciate your help. If you are currently using an ad blocker, please consider disabling it for our site. Thank you for your understanding and support.