Summary
The consensus is that PTR records and HELO/EHLO settings significantly impact email deliverability, although nuances exist. PTR records, essential for reverse DNS lookups, verify the sending server's identity by mapping its IP address to a domain name. While some experts suggest PTRs might not always be critical for large providers (like Google), smaller ISPs often scrutinize them more closely. HELO/EHLO strings, crucial for the SMTP handshake, should be valid, fully-qualified domain names (FQDNs) resolving to the sending server's IP. Generic HELO domains from ESPs can cause filtering issues, especially if the ESP's IPs are linked to spam. Proper configuration of both PTR records and HELO/EHLO settings builds trust, reduces the likelihood of emails being marked as spam, and improves overall inbox placement.
Key findings
- PTR for Verification: PTR records are vital for reverse DNS lookups, validating that the sending IP address is associated with a legitimate domain.
- HELO/EHLO Validation: The HELO/EHLO string needs to be a valid, resolvable domain name corresponding to the sending server.
- ISP Scrutiny: Smaller ISPs often pay closer attention to PTR record alignment than larger providers.
- Reputation Impact: Mismatches or improper configurations damage sender reputation, potentially lowering inbox placement rates and resulting in email rejection.
- Generic HELO Risks: Using generic HELO/EHLO domains, particularly from ESPs with spammy IPs, can trigger filtering problems.
Key considerations
- DNS Accuracy: Ensure accurate and consistent DNS records, including both forward and reverse DNS, to build trust.
- HELO Configuration: Configure the HELO/EHLO greeting with a valid, resolvable FQDN.
- Small ISP Compliance: Be mindful of PTR record requirements, particularly when sending to smaller ISPs.
- ESP HELO Policies: Evaluate your ESP's HELO policies, especially when using shared IPs, to prevent filtering issues.
- IP Strategy: Consider using a dedicated IP address for more control over PTR records and HELO/EHLO configurations if deliverability is paramount.
What email marketers say
11 marketer opinions
PTR records and HELO/EHLO greetings significantly impact email deliverability by establishing trust and verifying sender identity. Properly configured PTR records ensure reverse DNS lookups match the sending server's IP address to a legitimate domain, preventing emails from being flagged as spam. The HELO/EHLO greeting, a key part of the SMTP handshake, should be a valid, resolvable domain name associated with the sending server. Mismatches or poorly configured PTR records and HELO/EHLO greetings can damage sender reputation, lower inbox placement rates, and potentially lead to emails being rejected by receiving mail servers.
Key opinions
- PTR Records Essential: PTR records are crucial for reverse DNS lookups, verifying that the sending IP address is associated with a legitimate domain and preventing emails from being flagged as spam.
- HELO/EHLO Validation: The HELO/EHLO greeting must be a valid, resolvable domain name associated with the sending server to establish trust during the SMTP handshake.
- Impact on Reputation: Mismatches or improperly configured PTR records and HELO/EHLO greetings can damage sender reputation, leading to lower inbox placement rates and potential email rejection.
- Subdomain Recommendation: Using a subdomain of the sender domain for PTR records can further enhance deliverability, especially with Hotmail and iCloud.
Key considerations
- Ensure Correct Configuration: Verify that PTR records are properly configured to match the sending server's IP address and that the HELO/EHLO greeting matches a valid, resolvable domain name.
- Monitor Sender Reputation: Regularly monitor sender reputation to identify and address any issues related to PTR records and HELO/EHLO greetings that may be impacting deliverability.
- Dedicated IP vs. Shared IP: Consider using a dedicated IP address to have more control over PTR records and HELO/EHLO settings, especially if sending high volumes of email.
- Address HELO Reputation Issues: If using shared IPs, ensure that the HELO/EHLO domain isn't hurting deliverability due to the reputation of other senders on the same IP.
Marketer view
Email marketer from Stack Overflow suggests that the HELO setting should match your server's fully qualified domain name (FQDN). If it doesn't, some mail servers might reject your emails, especially those with stricter security policies.
1 Apr 2022 - Stack Overflow
Marketer view
Email marketer from SendGrid suggests that PTR records are essential for reverse DNS lookups, and they help verify that the sending IP address is associated with a legitimate domain. A valid PTR record can improve email deliverability by assuring receiving servers that the sender is not a spammer.
13 Jun 2024 - SendGrid
What the experts say
4 expert opinions
The impact of PTR records and HELO/EHLO on email deliverability is nuanced. While some experts suggest that PTR records might not always be critical (citing examples like Google), others emphasize their importance for reverse DNS lookups to verify sender authenticity. Similarly, the HELO/EHLO string should be a valid, fully-qualified domain name that resolves to the sending server's IP address. Using generic HELO domains from ESPs can lead to filtering problems, especially if the ESP's IPs are used for spam. Smaller ISPs may also be more strict about PTR record alignment.
Key opinions
- PTR Record Importance Varies: The necessity of PTR records can vary; some larger providers may not strictly enforce them, while smaller ISPs may be more stringent.
- HELO/EHLO String Validation: The HELO/EHLO string should be a valid, fully-qualified domain name that resolves to the sending server's IP address to avoid suspicion.
- Generic HELO Risks: Using generic HELO domains from ESPs can cause filtering problems, especially if the ESP's IPs are associated with spam.
- Reverse DNS Verification: PTR records are generally crucial for reverse DNS lookups to verify the authenticity of the sending server.
Key considerations
- Monitor ISP Requirements: Stay informed about the specific requirements of different ISPs regarding PTR records and HELO/EHLO configurations.
- Ensure Proper DNS Configuration: Verify that both forward and reverse DNS records are properly configured to avoid deliverability issues.
- Evaluate ESP HELO Policies: Carefully evaluate the HELO policies of your ESP, particularly if using shared IPs, to mitigate potential filtering problems.
- Consider Dedicated IPs: If deliverability is critical, consider using dedicated IPs for greater control over PTR records and HELO/EHLO configurations.
Expert view
Expert from Word to the Wise Laura Atkins answers that using a generic HELO/EHLO domain from ESPs can cause filtering problems, especially if the ESP’s IPs are used for sending spam, making it difficult to differentiate legitimate senders from malicious ones. Using a dedicated IP or ensuring that the HELO/EHLO is properly configured can improve deliverability.
29 Oct 2024 - Word to the Wise
Expert view
Expert from Spam Resource explains that the HELO/EHLO string should be a valid, fully-qualified domain name (FQDN) that resolves to the sending server's IP address. They add that using generic or non-resolvable HELO/EHLO strings can negatively impact deliverability as it appears suspicious to receiving mail servers.
20 May 2025 - Spam Resource
What the documentation says
4 technical articles
PTR records and HELO/EHLO are crucial for email deliverability. PTR records map IP addresses to domain names, verifying sender identity, while HELO/EHLO commands identify the SMTP client and should contain a valid, resolvable domain name. Accurate and consistent DNS records, including PTR and forward DNS, are essential for building trust with receiving mail servers and preventing emails from being flagged as spam. Proper PTR record setup is vital for reverse DNS lookups, ensuring mail servers can verify legitimacy.
Key findings
- PTR Record Verification: PTR records verify the identity of the sending server by mapping IP addresses to domain names.
- HELO/EHLO Identification: HELO/EHLO commands identify the SMTP client, and the domain name should be valid and resolvable.
- DNS Record Consistency: Maintaining consistent and accurate DNS records, including PTR and forward DNS, is essential for email deliverability.
- Reverse DNS Importance: PTR records are vital for reverse DNS lookups, allowing mail servers to verify legitimacy and prevent spam.
Key considerations
- Ensure Proper PTR Setup: Properly set up PTR records to ensure accurate reverse DNS lookups.
- Validate HELO/EHLO Domain: Ensure the domain name used in the HELO/EHLO command is valid and resolvable.
- Maintain DNS Accuracy: Regularly check and maintain the accuracy and consistency of DNS records, including PTR and forward DNS.
- Monitor for Mismatches: Monitor for any mismatches between IP addresses and domain names in PTR records, as well as any issues with HELO/EHLO configurations.
Technical article
Documentation from Microsoft Learn explains that a PTR record (reverse DNS lookup) maps an IP address to a domain name, and it is crucial for verifying the identity of the sending server. A mismatch or missing PTR record can negatively impact email deliverability, as it may cause the receiving mail server to flag the email as spam.
31 Jul 2021 - Microsoft Learn
Technical article
Documentation from RFC 5321 states that the HELO or EHLO command identifies the SMTP client to the SMTP server. The domain specified in HELO/EHLO should be a valid, resolvable domain name associated with the sending server. An improperly configured or missing HELO/EHLO can raise suspicion and harm deliverability.
6 Jun 2025 - RFC 5321
Does a sending IP address need to accept incoming SMTP connections for email deliverability?
How do I check if the sending IP address matches the IP address of the hostname specified in the Pointer (PTR) record?
How do I configure reverse DNS (rDNS) with multiple IP addresses for email sending?
How do I perform a reverse DNS lookup and interpret the results?
How does rDNS impact email deliverability when using dedicated IPs?
How important is it for reverse DNS to match SMTP banner for email deliverability?
What do PTR and HELO records mean in relation to AT&T email blocking, and whose responsibility are they?
