What’s the difference between IPv4 and IPv6 in email delivery?

Key differences for email:

Address space: IPv4 has about 4 billion addresses (exhausted). IPv6 has virtually unlimited addresses.

Reputation: IPv4 reputation is well-established. IPv6 reputation systems are newer and sparser.

Adoption: Most email still flows over IPv4. IPv6 adoption is growing but not universal.

Authentication:

SPF must include both IPv4 and IPv6 sending addresses.

PTR records needed for both protocols.

Delivery differences: Some receivers handle IPv6 differently. Reputation may not transfer between protocols.

Support both, but ensure IPv6 authentication and reputation are as robust as IPv4.

Two shipping lane systems. Most traffic uses the old lanes, but new lanes are increasingly important.