Opt-in to Enable or Disable IPv6 in Exchange Online (without DANE)
Starting October 16, 2024, Microsoft will enable IPv6 for all customer Accepted Domains using Exchange Online. This upgrade offers improved security, scalability, and performance by utilizing IPv6.
Organizations need to update their network allow-lists (Firewall) to permit Exchange Online IPv6 endpoints and modify any IP-based inbound connectors referencing IPv4 (Connector, Rules). It is possible to stay with IPv4-only traffic, domains can be opted out over a PowerShell cmdlet. After October 16, if no preference is set, IPv6 will be enabled by default, potentially affecting inbound email traffic.