What is the current state of IPv6 for email sending and what are the challenges and best practices?

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
9Marketer 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.

August 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.

November 2023 - Reddit
Marketer view

Email marketer from Email Vendor Guide recommends a gradual transition to IPv6. They suggest starting with a small percentage of IPv6 traffic and monitoring deliverability closely before increasing the volume. They also advocate for maintaining both IPv4 and IPv6 addresses to ensure maximum compatibility.

December 2023 - Email Vendor Guide
Marketer view

Email marketer from Mailjet explains that managing IP reputation on IPv6 can be different due to the vast address space. They suggest monitoring broader network segments and ensuring good sending practices across the entire allocated range to maintain a positive reputation.

May 2021 - Mailjet
Marketer view

Email marketer from GMass explains that like IPv4, IPv6 addresses need to be warmed up. They suggest starting with low volumes and gradually increasing the sending rate to build a positive reputation with mailbox providers.

April 2022 - GMass
Marketer view

Email marketer from EmailGeek Forums says that IPv6 is still on the horizon but hasn't become fully mainstream due to various technical and adoption challenges. They predict that as IPv4 addresses become scarcer, IPv6 adoption will likely increase.

November 2021 - EmailGeek Forums
Marketer view

Email marketer from SparkPost shares that IPv6 adoption in email is growing but still limited. They explain that while IPv6 offers benefits like larger address space, challenges include inconsistent support among ISPs and the need for senders to manage both IPv4 and IPv6 reputations. They also mention that many ISPs still rely heavily on IPv4 for filtering and reputation.

May 2021 - SparkPost
Marketer view

Email marketer from StackOverflow shares that one challenge is that some anti-spam systems aren't fully updated for IPv6 ranges and reputation tracking, potentially leading to false positives or deliverability problems. They suggest checking with major mailbox providers on their IPv6-specific guidelines.

June 2024 - StackOverflow
Marketer view

Marketer from Email Geeks estimates that IPv6 mail is about 5-10% of daily inbound, including major providers like Google, Outlook, LinkedIn, and Facebook. Alex also confirms that ~7% of mail is over IPv6, with ~80% of mail being promotional/ESP-sent.

April 2023 - Email Geeks

What the experts say
9Expert 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.

September 2021 - 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.

August 2023 - Email Geeks
Expert view

Expert from Email Geeks, Laura Atkins (she/her), notes that Spamhaus blocks by /64, which is the minimum IPv6 allocation, and that it annoys people using OVH. The reason for this is because OVH is doing something wrong and if they followed standard practice then their non-spamming customers wouldn't be suffering due to their spammy customers. Alex then chimed in to recommend choosing a better provider, given there are so many reasons to avoid OVH.

September 2021 - Email Geeks
Expert view

Expert from Email Geeks mentions current challenges of sending over IPv6 like blocklists and IP resolution due to bad network neighborhoods, making it potentially more problematic than IPv4 due to the vastness of IPv6 space and ease of IP jumping.

October 2021 - Email Geeks
Expert view

Expert from Email Geeks shares that getting your own IPv4 range is another option, stating that she's helped a lot of clients with it.

December 2021 - Email Geeks
Expert view

Expert from Email Geeks suggests that an ESP with good planning skills should consider sending as much mail as possible via dedicated IPv6 with a fallback to a smaller pool of IPv4, or at least test this approach on a small scale.

December 2022 - Email Geeks
Expert view

Expert from Email Geeks agrees that IP address reputation is poorly suited to email filtering and mostly doesn't matter with a minimum good reputation, noting that she has thought this for a long time.

June 2023 - Email Geeks
Expert view

Expert from Spam Resource emphasizes the importance of having correct reverse DNS (PTR records) for IPv6 addresses. He explains that many mail servers reject connections from IPv6 addresses without proper reverse DNS, as it's a common characteristic of spam sources.

January 2024 - Spam Resource
Expert view

Expert from Word to the Wise responds by saying that, IP reputation is important, but for IPv6, consider reputation on the /64 level. She highlights that while IPv6 provides a vast address space, reputation is often assessed at the /64 subnet level, and maintaining good reputation across this subnet is critical for deliverability.

April 2023 - Word to the Wise

What the documentation says
4Technical 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.

October 2024 - 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.

June 2024 - Microsoft
Technical article

Documentation from Internet Engineering Task Force (IETF) specifies that RFC 8314 recommends that all Internet mail be transmitted via IPv6 wherever possible, though IPv4 is still heavily used and remains critical for interoperability. It emphasizes using both IPv6 and IPv4 during the transition period.

July 2024 - Internet Engineering Task Force (IETF)
Technical article

Documentation from Google Postmaster Tools specifies that while Google supports IPv6, senders must ensure proper authentication (SPF, DKIM, DMARC) for their IPv6 addresses. It also highlights that reputation is still crucial and that IPv6 senders are subject to the same spam filtering rules as IPv4 senders.

February 2024 - Google

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