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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.