Can sending email from IPv4 cause delivery issues to IPv6 recipients, and how can I ensure compatibility?
Summary
What email marketers say11Marketer opinions
Email marketer from MailChannels highlights the importance of having a good IPv6 reputation for deliverability. Monitoring tools are necessary.
Email marketer from SparkPost shares that IPv6 should not directly impact email deliverability negatively. However, the reputation of the IPv6 address is important. Monitor and manage your IPv6 address reputation.
Email marketer from EmailonAcid discusses IP warming as relevant to IPv6 addresses. To maintain a good reputation, start with low sending volumes on new IPv6 addresses and gradually increase them.
Email marketer from SendGrid emphasizes the importance of having correct rDNS entries for IPv6 addresses, as these contribute towards a good reputation.
Email marketer from ServerFault mentions that IPv6 itself shouldn't cause delivery problems if both sender and receiver are configured correctly. Issues arise when IPv6 reputation is poor or reverse DNS is misconfigured.
Email marketer from Port25 Solutions suggests ensuring your sending infrastructure supports both IPv4 and IPv6. Monitor reputation of your sending IPs and domains over both protocols to ensure no delivery issues
Marketer from Email Geeks shares that from an anti-abuse perspective, there are nuanced problems with vastly different sizes of IPv6 space that can be abused, making reliance on domain reputation more important.
Email marketer from Google Workspace Admin Help explains that IPv6 should not directly cause delivery issues. Google's servers support both IPv4 and IPv6, and they handle the translation between the two protocols. However, reputation issues on IPv6 ranges could affect delivery.
Email marketer from MXToolbox details that if sending from IPv4 and recipients are IPv6, there shouldn't be issues as long as standard protocols are followed. Use tools to check DNS records (A and AAAA) and reverse DNS to ensure proper setup.
Email marketer from Mailjet notes that IP warming practices are vital for new IPv6 sending IPs. Gradually increasing the volume is essential.
Email marketer from Reddit shares that setting up proper DNS records (A and AAAA) and ensuring correct reverse DNS is crucial for IPv6 mail server compatibility. Poor IPv6 reputation can lead to delivery issues.
What the experts say11Expert opinions
Expert from SpamResource explains that as long as you implement IPv6 correctly (including rDNS), sending from IPv4 to IPv6 recipients shouldn't be an issue. Incorrect IPv6 configurations and poor IPv6 reputation are the main causes for deliverability problems.
Expert from Email Geeks explains that you can have a reasonable setup on IPv4 that delivers fine, but if you were to do the same thing on IPv6 it wouldn’t.
Expert from Email Geeks discusses a time when IPv6 had an advantage because large consumer MBPs had excess IPv6 capacity, making throttling less likely. He doubts that's the case today.
Expert from Email Geeks says you need a working IPv6 production network and IPv6 configured on the PMTA box. While there are slight advantages to supporting mail over IPv6, they’re minor.
Expert from Email Geeks shares that there are some challenges to sending over IPv6 that don't come up with IPv4, but the spread is getting less intense.
Expert from Email Geeks says some mailbox providers hold mail from IPv6 sources to higher standards than IPv4.
Expert from Email Geeks mentions Google being a big example of a provider that used to have higher standards for IPv6 but it was more evident before the new authentication / alignment requirements from 2023.
Expert from Word to the Wise suggests that while IPv6 connectivity should not directly cause deliverability problems, IPv6 reputation and configuration are critical. Monitor your IPv6 reputation and ensure you've configured rDNS correctly.
Expert from Email Geeks says it's harder to send over IPv6 and that the requirements for sending over IPv4 are a little different than the requirements of IPv6.
Expert from Email Geeks explains that aboutmy.email has two MXes, one IPv6 and one IPv4. Compliant mail servers will attempt IPv4 delivery only if IPv6 fails. He says it's likely the user cannot deliver mail over IPv6 but notes very few mailbox providers are IPv6 only.
Expert from Email Geeks notes that with IPv6, you potentially have more information about the sender (e.g., 100 customers on different addresses in a /64 vs. a single IPv4 address).
What the documentation says4Technical articles
Documentation from Postfix explains that Postfix supports IPv6. Configuration involves setting up the appropriate network interfaces and ensuring DNS records are correctly configured for IPv6 addresses.
Documentation from Cisco recommends dual-stack configurations for IPv6 transition. This ensures that systems can communicate over both IPv4 and IPv6 networks, maintaining compatibility.
Documentation from RFC 6145 details various IPv6 transition mechanisms including dual-stack implementations. Dual-stack allows mail servers to communicate using both IPv4 and IPv6, ensuring compatibility regardless of the recipient's network.
Documentation from Microsoft Learn explains that Exchange Server supports IPv6. Ensure Exchange is properly configured for IPv6, including DNS records and network settings, to prevent delivery issues to IPv6 recipients.