Summary
Even when using SPF, IPv6 emails often end up in spam due to a confluence of factors. DKIM and DMARC are crucial for establishing trust and authenticating IPv6 emails, as legacy systems may not fully trust IPv6 based solely on SPF. Reputation plays a significant role, with ISPs often assigning reputation to larger IPv6 blocks, meaning a small part of a block's poor activity can affect the entire range. Older spam filters may not fully support IPv6, and some ISPs have inconsistent IPv6 support. New IPv6 addresses require careful warm-up to build a positive reputation. Content can trigger spam filters, and maintaining good list hygiene is essential. Reverse DNS (PTR) records need to be properly configured. Monitoring tools like Google Postmaster Tools and Microsoft SNDS can help identify deliverability issues, and checking against blocklists is recommended.
Key findings
- DKIM/DMARC Essential: DKIM and DMARC are nearly mandatory for IPv6 to achieve good deliverability due to stricter authentication requirements.
- Reputation Scope: IPv6 reputation is often assigned to larger address blocks (/56 or larger), affecting the deliverability of the entire block.
- Legacy Systems: Legacy systems may not fully trust IPv6 with SPF alone, requiring stronger authentication methods.
- New IP Warm-up: A careful warm-up process is essential to establish a positive reputation for new IPv6 addresses.
- List Hygiene: Poor list hygiene can negatively impact IPv6 reputation and increase the likelihood of spam filtering.
Key considerations
- Implement DKIM/DMARC: Implement and properly configure DKIM and DMARC for your IPv6 sending domain.
- Monitor Reputation: Regularly monitor the reputation of your entire IPv6 address range using available tools.
- Configure PTR Records: Ensure that your IPv6 address has a properly configured reverse DNS (PTR) record that matches your sending domain.
- Warm-up Gradually: Start with a very low sending volume and gradually increase it over time to warm up new IPv6 addresses.
- Maintain List Hygiene: Regularly clean your email list to remove invalid and unengaged addresses.
- Check Blocklists: Periodically check your IPv6 address against known blocklists.
- Review Content: Check email content, including links and formatting, for potential spam triggers.
- Use Monitoring Tools: Utilize Google Postmaster Tools and Microsoft SNDS to monitor your IPv6 deliverability.
What email marketers say
10 marketer opinions
Even with SPF in place, IPv6 emails often land in spam due to factors such as strict enforcement of authentication (DKIM and DMARC), poor or new IP reputation, older spam filters not fully supporting IPv6, issues with reverse DNS records (PTR), content triggering filters, inadequate IP warmup, ISP inconsistencies, and poor list hygiene.
Key opinions
- Authentication: DKIM and DMARC are crucial for IPv6 deliverability, often more so than for IPv4.
- Reputation: IPv6 address reputation is a significant factor, with new or shared ranges often having a lower score.
- Reverse DNS: Properly configured reverse DNS (PTR) records are essential for IPv6 addresses.
- Spam Filters: Older spam filters may not fully support IPv6, leading to misclassification.
- Content Sensitivity: Content filters can be more sensitive with new or less reputable IPv6 addresses.
- IP Warmup: New IPv6 addresses require a 'warmup' period to establish a positive sending reputation.
- List Hygiene: Poor list hygiene negatively impacts IPv6 reputation and increases spam filtering.
Key considerations
- Implement DKIM/DMARC: Ensure DKIM and DMARC are correctly configured alongside SPF.
- Monitor Reputation: Actively monitor the reputation of your IPv6 address range.
- Configure PTR Records: Verify that your IPv6 address has a properly configured reverse DNS record.
- IP Warmup: Gradually increase sending volume from new IPv6 addresses.
- Segment and Test: Segment your list and test deliverability with smaller volumes of IPv6 email.
- Review Content: Review email content for spam triggers.
- List Hygiene: Maintain a clean and engaged email list.
Marketer view
Email marketer from Marketing Discussions shares that poor list hygiene (sending to old, invalid, or unengaged email addresses) can hurt your IPv6 reputation and cause spam filtering. Always maintain a clean and engaged email list.
2 May 2025 - Marketing Discussions
Marketer view
Email marketer from Email Marketing Forum mentions the importance of having a properly configured reverse DNS (PTR) record for the IPv6 address, matching the sending domain. A missing or incorrect PTR record can negatively impact deliverability.
21 Mar 2025 - Email Marketing Forum
What the experts say
3 expert opinions
Experts agree that IPv6 emails often land in spam despite SPF due to a combination of factors. IPv6 reputation is crucial and applies to larger address blocks (/56 or bigger), so monitoring the entire range is important. Authentication is also strictly enforced, making DKIM and DMARC almost mandatory for deliverability. While content and mailstream reputation are important, IPv6 has no legacy support for unauthenticated mail.
Key opinions
- IPv6 Reputation Range: IPv6 reputation applies to larger address blocks (/56 or bigger), affecting the entire range.
- Strict Authentication: Authentication is more strictly enforced on IPv6; DKIM and DMARC are almost mandatory.
- No Legacy Support: IPv6 lacks legacy support for unauthenticated mail, unlike IPv4.
Key considerations
- Range Monitoring: Carefully monitor the reputation of your entire IPv6 address range.
- Implement DKIM/DMARC: Ensure DKIM and DMARC are correctly configured for IPv6 sending.
- Mailstream and Content: Pay attention to mailstream and content reputation in addition to IPv6 specific factors.
Expert view
Expert from Email Geeks explains that IPv6 does have a reputation, usually applying to at least /56s, and probably bigger. Also, since there are no legacy IPv6 sources of mail there's no need to support unauthenticated mail from IPv6. However, similar to IPv4, it's less important than mailstream and content reputation.
19 Mar 2022 - Email Geeks
Expert view
Expert from Spam Resource, John Levine, responds that one reason IPv6 emails go to spam is that IPv6 address blocks are often assigned in larger chunks than IPv4, and if a small part of a block gets a bad reputation, the entire block can be affected. He recommends carefully monitoring the reputation of your entire IPv6 range.
15 Jan 2024 - Spam Resource
What the documentation says
6 technical articles
Even with SPF, IPv6 emails often land in spam because legacy systems may not fully trust IPv6 without DKIM. Maintaining a positive sender reputation is crucial, and IPv6 addresses are treated similarly to IPv4 addresses regarding reputation. Anti-spam best practices include robust authentication (SPF, DKIM), accurate reverse DNS records, and volume control. Checking against blocklists, like those maintained by Spamhaus, and using tools like Google Postmaster Tools and Microsoft SNDS for monitoring, can help identify and resolve deliverability issues. Implementing DMARC is recommended for enhanced trust and prevention of email spoofing.
Key findings
- DKIM Crucial: DKIM is essential for IPv6 deliverability, as legacy systems may not fully trust IPv6 without it.
- Reputation Matters: A positive sender reputation, including IPv6 reputation, is vital for inbox placement.
- Authentication: Robust authentication techniques (SPF, DKIM) and accurate reverse DNS records are recommended.
- Blocklist Checks: Being listed on IPv6 blocklists, such as those maintained by Spamhaus, can cause deliverability issues.
- Monitoring Tools: Tools like Google Postmaster Tools and Microsoft SNDS help identify and resolve IPv6 deliverability issues.
- Implement DMARC: Implementing DMARC improves trust with ISPs and prevents email spoofing.
Key considerations
- Implement DKIM: Implement DKIM in addition to SPF for IPv6 email.
- Monitor Reputation: Monitor your IPv6 reputation using available tools.
- Check Blocklists: Regularly check your IPv6 address against blocklists.
- Configure rDNS: Ensure accurate reverse DNS records are set up for your IPv6 address.
- Use Monitoring Tools: Utilize Google Postmaster Tools and Microsoft SNDS to identify issues.
- Implement DMARC: Implement DMARC for enhanced security and trust.
Technical article
Documentation from Google Postmaster Tools explains that while SPF is a good start, DKIM is crucial for IPv6, especially since many legacy systems may not fully trust IPv6 without it. Also, monitor spam rates via Postmaster Tools to identify any deliverability issues specific to IPv6.
9 Mar 2022 - Google
Technical article
Documentation from Microsoft SNDS shares that they use their own reputation system, and IPv6 addresses are treated like any other IP. It advises regularly checking the SNDS portal for any issues related to your sending IPs, including IPv6.
20 Jul 2022 - Microsoft
Can sending email from IPv4 cause delivery issues to IPv6 recipients, and how can I ensure compatibility?
Does unaligned SPF affect Gmail performance and domain reputation?
How do I properly set up SPF and DKIM records for email marketing, including handling multiple SPF records, IP ranges, bounce capturing, and Google Postmaster Tools verification?
How do SPF, DKIM, and DMARC email authentication standards work?
What are SPF, DKIM, and DMARC, and when are they needed?
Why am I seeing Gmail SPF error messages and how do I fix it?
