Summary
PTR records (Reverse DNS) map IP addresses to domain/hostnames, validating that a server is authorized to send email from that domain. The HELO/EHLO commands initiate an SMTP session, identifying the sending server. A mismatch between the hostname in the HELO/EHLO command and the hostname associated with the IP address in the PTR record can lead to deliverability problems, including being blocked by ISPs like AT&T. Using a real domain name in the HELO/EHLO command is vital. Generally, the ISP, hosting provider, or ESP is responsible for managing PTR records. Maintaining proper reverse DNS helps build a positive IP reputation and prevent spoofing, improving overall email deliverability. If using EC2, you are responsible; otherwise, contact your ISP. There may be other, unrevealed factors AT&T uses when deciding to block email traffic. It's often more important to avoid negative impacts to IP reputation than to ensure positive ones.
Key findings
- PTR Definition: PTR records resolve IP addresses to hostnames, enabling reverse DNS lookups and server validation.
- HELO/EHLO Function: HELO/EHLO initiates the SMTP handshake and identifies the sending server.
- Hostname Mismatch: A mismatch between HELO/EHLO hostname and PTR record can result in deliverability issues, including blocking.
- Responsibility: PTR record management typically falls to the ISP, hosting provider, or ESP (unless using EC2).
- Reputation Impact: Proper reverse DNS configuration is crucial for IP reputation and avoiding spam filters. Avoiding negative impacts is paramount.
- EC2 Exception: When sending from EC2, the user is responsible for setting up the reverse DNS.
- Domain Validation: HELO/EHLO domain must be a valid, existing domain.
Key considerations
- Authorize Domain: Verify the domain is authorized to send from the server's IP address.
- Consistent Hostname: Ensure the hostname used in HELO/EHLO matches the domain name and the PTR record.
- ISP Contact: Consult your ISP/ESP about configuring PTR records and HELO/EHLO settings.
- Deliverability Monitoring: Monitor email deliverability to identify and address issues early.
- Reputation Management: Focus on preventing actions that could negatively impact your IP's reputation.
- EC2 Configuration: If using EC2, take full ownership of your reverse DNS configuration.
- Aknowledgement: Acknowledging there may be other red flags the ESP provider has.
What email marketers say
10 marketer opinions
PTR records map IP addresses to hostnames, while HELO/EHLO provide the sending server's hostname. AT&T, like many ISPs, may block emails if there's a mismatch between the hostname presented in HELO/EHLO and the hostname associated with the IP address via the PTR record. This mismatch can flag emails as spam. The responsibility for managing PTR records typically lies with the ISP, hosting provider, or ESP that owns the IP address block. Ensuring your HELO resolves to a valid DNS address is also important. PTR records help build trust and improve email deliverability by confirming the mail server's authenticity and preventing spoofing.
Key opinions
- PTR Definition: PTR records map IP addresses to hostnames, enabling reverse DNS lookups.
- HELO/EHLO Purpose: HELO/EHLO commands provide the sending server's hostname during the SMTP handshake.
- Mismatch Issues: A mismatch between HELO/EHLO hostname and PTR record can lead to deliverability problems and potential blocking.
- Responsibility: PTR record management is generally the responsibility of the ISP, hosting provider, or ESP.
- Deliverability Impact: Properly configured PTR and HELO/EHLO are crucial for email deliverability, verifying server identity, and avoiding spam filters.
Key considerations
- PTR Record Accuracy: Ensure your PTR record accurately reflects the hostname of your sending server.
- HELO Consistency: Use a consistent and valid hostname in the HELO/EHLO command that resolves to a real domain.
- Contacting Your Provider: If you don't manage your own IP addresses, work with your ISP or ESP to ensure PTR records are correctly configured.
- Monitoring Deliverability: Regularly monitor your email deliverability to identify and address any PTR/HELO-related issues.
- Other Red Flags: Be aware that AT&T or other ISPs might use these checks in addition to other less transparent metrics to determine blocking policies.
Marketer view
Email marketer from Email On Acid explains that PTR records play a role in increasing email deliverability because many servers will automatically reject messages from servers without one. Ensuring your mail server has a PTR record ensures they can verify the sending server.
11 Jul 2024 - Email On Acid
Marketer view
Email marketer from Stack Overflow explains that the responsibility for PTR records usually lies with the owner of the IP address block. This is typically the ISP or hosting provider. If you are using an ESP, they will manage the PTR records for their sending IPs.
30 Aug 2021 - Stack Overflow
What the experts say
4 expert opinions
PTR records link IPs to hostnames, and HELO initiates the SMTP connection. A mismatch between the hostname presented in HELO and the hostname associated with the IP in the PTR record, especially if HELO is a non-existent domain, can lead to AT&T blocking the email. The ESP (Email Service Provider) usually handles these configurations. Maintaining valid reverse DNS is important for your IP reputation, and it is generally more important to avoid negative impacts in this area than guaranteeing positive ones.
Key opinions
- PTR Record: Maps IP addresses to hostnames (reverse DNS).
- HELO Command: Initiates SMTP session and presents the hostname of the sending server.
- Mismatch Issue: A discrepancy between HELO and PTR record can lead to blocking.
- ESP Responsibility: The ESP is typically responsible for managing these configurations.
- HELO Domain: The HELO domain needs to be a real and valid domain.
- Impacts: Avoiding negative impacts on the HELO domain is more important than guaranteeing positive ones.
Key considerations
- Reverse DNS Validation: Verify that the hostname resolves to a valid domain.
- ESP Coordination: Work closely with your ESP to ensure correct configuration.
- HELO Domain Authenticity: Use a real and valid domain for the HELO command.
- Reputation Maintenance: Prioritize avoiding issues that would negatively impact your reputation.
- Address Accuracy: Ensure the PTR records are setup accurately.
Expert view
Expert from Email Geeks explains that PTR record says which IP belongs to which hostname and HELO is the first step in SMTP. AT&T is saying the hostname in the PTR record differs from what the machine introduces itself as.
29 Oct 2021 - Email Geeks
Expert view
Expert from Spam Resource explains that your HELO domain is critically important, it needs to be a real domain, not a made up name.
28 Dec 2024 - Spam Resource
What the documentation says
4 technical articles
PTR records (Reverse DNS) map IP addresses to domain/hostnames, verifying the sender's authorization. HELO/EHLO initiate SMTP sessions, identifying the sending client and enabling protocol extension negotiation. Using a consistent hostname in HELO/EHLO and ensuring a matching PTR record improves deliverability. If sending from EC2, setting up reverse DNS is your responsibility; otherwise, contact your ISP.
Key findings
- PTR Records Defined: PTR records resolve IP addresses to domain/hostnames for reverse DNS lookups.
- HELO/EHLO Function: HELO/EHLO initiates SMTP sessions and identifies the sending client.
- Hostname Consistency: Using a consistent hostname in HELO/EHLO and matching PTR record enhances deliverability.
- EC2 Responsibility: Setting up reverse DNS is your responsibility when sending from EC2.
Key considerations
- Authorize Domain: Authorise domain name to send from.
- Consistent Hostname: Make hostname used match the domain name and hostname in PTR record.
- ISP Contact: Contact your ISP about configuring PTR records.
Technical article
Documentation from AWS shares that, in regards to reverse DNS records, if you send email from EC2, it is your responsibility to set up the reverse DNS records for your IP addresses. Contact your ISP if it is not AWS.
7 Dec 2024 - Amazon Web Services
Technical article
Documentation from Google Postmaster Tools recommends using a consistent hostname in the HELO or EHLO command, and ensuring that a PTR record exists for the sending IP address that matches this hostname. This helps improve email deliverability.
19 Sep 2021 - Google Postmaster Tools
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