Starting October 1, 2024, Microsoft announced that it will begin gradually enabling IPv6 for all Accepted Domains using Exchange Online for inbound mail. This update aims to modernize Exchange Online and provide improved security and performance, while also helping customers comply with local regulations.
Impact
Once IPv6 is enabled for your Accepted Domains, email senders will receive both IPv4 and IPv6 addresses when querying the MX record for your domain.
Preparation
To benefit from IPv6, ensure your network allow-lists Exchange Online IPv6 endpoints, similar to how you handle IPv4. You can find the IPv6 endpoints in the Microsoft 365 URLs and IP address ranges.
Opting Out?
If you prefer to remain IPv4-only, stay tuned for an update in September with instructions on how to opt-out of IPv6.
Authentication
Note that traffic over IPv6 will come with stricter authentication requirements. More details are available in the Support for anonymous inbound email over IPv6 documentation.
Stay prepared for this update to ensure a smooth transition!
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