Summary
The current state of IPv6 for email sending is one of growing adoption, but with significant challenges and best practices that must be considered. While IPv6 offers a vast address space and is technically viable, its adoption is still limited, with estimates placing IPv6 email traffic at approximately 5-10% of total email volume. Experts recommend a balanced approach, suggesting ESPs consider sending as much mail as possible via dedicated IPv6 with a fallback to a smaller pool of IPv4. A gradual transition is advised, starting with a small percentage of IPv6 traffic and closely monitoring deliverability. Technical documentation emphasizes the need for proper authentication (SPF, DKIM, DMARC) for IPv6 senders. Good IP reputation remains crucial, and senders should monitor IPv6 sending reputation separately from IPv4, considering reputation on the /64 level. Challenges include inconsistent support among ISPs, legacy systems in smaller organizations that may not fully support IPv6, and some anti-spam systems not fully updated for IPv6 ranges. Other best practices include maintaining consistent reverse DNS records, avoiding blocklists, warming up IPv6 addresses like IPv4 addresses, and ensuring updated security appliances and intrusion detection systems.
Key findings
- Limited Adoption: IPv6 adoption in email is growing, but still limited to a small percentage of total traffic (around 5-10%).
- Inconsistent Support: Inconsistent support among ISPs and legacy systems hinder full IPv6 adoption.
- Authentication Critical: Proper authentication (SPF, DKIM, DMARC) is essential for IPv6 senders.
- Reputation Matters: Good IP reputation and monitoring are crucial for IPv6 deliverability.
- Address Importance: Maintaining correct reverse DNS records is important for IPv6 addresses.
- Filtering Immaturity: Some anti-spam systems are not fully updated for IPv6 ranges, leading to potential filtering issues.
- IPv6 Advantage: IPv6 is cheaper and quicker to deploy than IPv4.
Key considerations
- Gradual Transition: Implement a gradual transition to IPv6, starting with a small traffic percentage.
- Dual Addressing: Maintain both IPv4 and IPv6 addresses for maximum compatibility during transition.
- Authentication Setup: Ensure proper authentication (SPF, DKIM, DMARC) is configured for IPv6 sending.
- Reputation Monitoring: Monitor IPv6 sending reputation separately from IPv4, particularly at the /64 subnet level.
- ISP Guidelines: Check with major mailbox providers for their IPv6-specific sending guidelines.
- Infrastructure Updates: Update security appliances and intrusion detection systems for IPv6 traffic.
- Blocklist Monitoring: Monitor your IPv6 address ranges on the various blocklists.
- Address Warmup: Warm up IPv6 sending by sending a small traffic volume before increasing.
What email marketers say
9 marketer opinions
While IPv6 adoption in email is growing, it remains limited, accounting for a small percentage of total email traffic (around 5-10%). Challenges include inconsistent support among ISPs, the need to manage separate IPv4 and IPv6 reputations, and the fact that many anti-spam systems are not fully updated for IPv6. Best practices involve a gradual transition, starting with a small percentage of IPv6 traffic and closely monitoring deliverability. Maintaining both IPv4 and IPv6 addresses ensures maximum compatibility, and senders should warm up their IPv6 addresses like IPv4 addresses, beginning with low volumes and gradually increasing the sending rate. Ensuring proper authentication and monitoring reputation across broader network segments are also essential for maintaining deliverability.
Key opinions
- Adoption Rate: IPv6 email traffic accounts for a small percentage (5-10%) of total email volume.
- Inconsistent Support: ISPs exhibit inconsistent support for IPv6, creating deliverability challenges.
- Legacy Systems: Many smaller organizations still rely on legacy systems that don't fully support IPv6.
- Anti-Spam Issues: Some anti-spam systems aren't fully updated for IPv6 ranges, leading to potential filtering problems.
- ISP Optimization: ISPs may not have optimized their filtering systems for IPv6 email.
Key considerations
- Gradual Transition: Implement a gradual transition to IPv6, starting with a small traffic percentage.
- Dual Addressing: Maintain both IPv4 and IPv6 addresses for maximum compatibility.
- Address Warmup: Warm up IPv6 addresses with low sending volumes before increasing the rate.
- Reputation Management: Monitor reputation across broader IPv6 network segments.
- Authentication: Ensure proper authentication (SPF, DKIM, DMARC) for IPv6 sending.
- Mailbox Provider Guidelines: Check with major mailbox providers for their IPv6-specific sending guidelines.
Marketer view
Email marketer from Quora says that one of the biggest challenges is that some ISPs are slow to fully implement IPv6, and their filtering systems may not be fully optimized for IPv6 email, which can cause deliverability issues even for legitimate senders.
10 Nov 2023 - Quora
Marketer view
Email marketer from Reddit shares that while IPv6 is technically viable, the biggest hurdle is that not all receiving mail servers are equally equipped to handle it, leading to potential deliverability issues. They note that many smaller organizations still rely on legacy systems that may not fully support IPv6.
27 Sep 2024 - Reddit
What the experts say
9 expert opinions
Experts generally agree that while IPv6 functions well with many mailbox providers and offers a vast address space, it's not without its challenges. Proper authentication is crucial, and relying solely on IPv6 is discouraged. A balanced approach, leveraging IPv6 where possible with a fallback to IPv4, is advised. Obtaining your own IPv4 range is also a viable option. Managing reputation in IPv6 differs, with reputation often assessed at the /64 subnet level. IP reputation, in general, is becoming less significant, but correct reverse DNS is essential. Blocklisting and network neighborhoods can pose issues. Providers like OVH, with non-standard IPv6 allocations, can cause deliverability problems.
Key opinions
- IPv6 Functionality: IPv6 works well with many mailbox providers but requires modern authentication.
- Address Space: IPv6 provides a significantly larger address space compared to IPv4.
- Reputation Management: IPv6 reputation is often assessed at the /64 subnet level.
- Reverse DNS: Correct reverse DNS (PTR records) are essential for IPv6 addresses.
- Blocklisting: Poor network neighborhoods and blocklisting can impact IPv6 deliverability.
- OVH Issues: OVH's non-standard IPv6 allocation practices can lead to deliverability problems.
Key considerations
- Balanced Approach: Adopt a balanced approach, leveraging IPv6 where possible with IPv4 as a fallback.
- Authentication: Ensure proper authentication for IPv6 email sending.
- Reputation: Consider reputation on the /64 level when sending via IPv6.
- Reverse DNS: Ensure you have correctly setup reverse DNS on IPv6 sending.
- Provider Selection: Choose reputable providers that adhere to standard IPv6 allocation practices.
- IPv4 Alternative: Consider getting your own IPv4 range
Expert view
Expert from Email Geeks, Steve Atkins (WttW), mentions how it’s much cheaper, easier, and quicker to get a /64 IPv6 burner address than a single IPv4 address. Then Laura Atkins (she/her) added, there are more IPs in a /64 (the smallest allocated amount) than in all of IPv4. You could basically send one message per IP and never run out of IPs. Steve also noted that filtering or tracking reputation wouldn't be based on single IPs.
23 May 2023 - Email Geeks
Expert view
Expert from Email Geeks explains that IPv6 works fine at many mailbox providers, with caveats about requiring modern authentication, but not all, advising caution about being IPv6-only.
9 May 2025 - Email Geeks
What the documentation says
4 technical articles
Technical documentation suggests that while IPv6 is the recommended direction for internet mail transmission, IPv4 remains critical for interoperability, particularly during the transition. Proper authentication (SPF, DKIM, DMARC) is essential for IPv6 senders, and good IP reputation remains crucial, subject to similar spam filtering rules as IPv4. Maintaining consistent reverse DNS records and avoiding blocklists are important, along with monitoring IPv6 sending reputation separately. Securing IPv6 email traffic necessitates updated security appliances and intrusion detection systems.
Key findings
- IPv6 Recommendation: IETF recommends IPv6 for Internet mail transmission.
- IPv4 Importance: IPv4 remains critical for interoperability, especially during transition.
- Authentication Required: Proper authentication (SPF, DKIM, DMARC) is essential for IPv6.
- Reputation Matters: Good IP reputation is crucial for IPv6, similar to IPv4.
- Security Updates: Securing IPv6 traffic requires updated security appliances and systems.
Key considerations
- Dual Support: Use both IPv6 and IPv4 during the transition period.
- Authentication Setup: Ensure proper authentication (SPF, DKIM, DMARC) for IPv6 addresses.
- Reputation Monitoring: Monitor IPv6 sending reputation separately from IPv4.
- Reverse DNS: Maintain consistent reverse DNS records for IPv6.
- Blocklist Avoidance: Ensure IPv6 IPs are not listed on blocklists.
- Security Upgrade: Update security appliances and intrusion detection systems for IPv6.
Technical article
Documentation from Cisco Security Team specifies that securing IPv6 email traffic requires updated security appliances and software to handle IPv6 addresses and protocols. They also recommend implementing intrusion detection and prevention systems capable of analyzing IPv6 traffic.
13 Apr 2022 - Cisco
Technical article
Documentation from Microsoft Exchange Team outlines that IPv6 senders should maintain consistent reverse DNS records and ensure their IPs are not listed on blocklists. The documentation also stresses the importance of monitoring IPv6 sending reputation separately from IPv4, as different metrics may apply.
31 Jan 2024 - Microsoft
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