How can I check my PTR and HELO records?

You can typically check your PTR record by performing a reverse DNS lookup using various online tools, often by entering your IP address. To check your HELO string, you would usually need to access your mail server's configuration or examine the raw headers of an email sent from your server. The HELO/EHLO command appears early in the email headers, usually after the 'Received:' lines.

Do PTR records need to match my sending domain exactly?

While not always strictly required by all receiving servers, it is a strong best practice for your PTR record to resolve to a subdomain of your sending domain (e.g., mail.yourdomain.com). This alignment adds credibility and helps establish trust with more stringent email providers and anti-spam systems.

What happens if my PTR or HELO records are misconfigured?

Misconfigured PTR or HELO records can severely impact deliverability. Your emails may be flagged as spam, sent to junk folders, or rejected outright by receiving mail servers. This happens because these records serve as basic authentication checks, and their failure raises suspicion about the sender's legitimacy.

Are PTR and HELO records sufficient for email authentication?

No, PTR and HELO records are foundational but not sufficient for comprehensive email authentication. They are often complemented by other crucial authentication protocols like SPF, DKIM, and DMARC. These work together to provide a robust framework for verifying sender identity and preventing spoofing and phishing.

How do major email providers like Google and Microsoft view these records?

Major email providers like Google, Microsoft, and Apple all consider PTR and HELO records as part of their reputation assessment, though their strictness can vary. A properly configured PTR and an aligned HELO contribute positively to your sender reputation and increase the likelihood of inbox delivery, especially with services that apply stricter anti-spam filters.

Do PTR records and HELOs impact email deliverability? - Technical - Email deliverability - Knowledge base

Email deliverability is a complex puzzle, with many pieces contributing to whether your messages land in the inbox or the spam folder. Among the foundational elements that influence this outcome are PTR records and HELO commands. These technical configurations, often behind the scenes, play a significant role in how receiving mail servers perceive the legitimacy of your sending infrastructure.

Understanding their function and ensuring they are correctly configured can make a substantial difference in your email campaigns. This includes knowing what PTR records are and how the reverse DNS matches the SMTP banner.

The role of PTR records

A PTR record, or Pointer Record, is a type of DNS record that performs the reverse function of an A record. While an A record translates a domain name into an IP address, a PTR record translates an IP address back into a domain name. This process is known as Reverse DNS (rDNS) lookup. When an email server receives an incoming connection, it often performs an rDNS lookup on the connecting IP address.

The primary purpose of PTR records in email deliverability is to verify the legitimacy of the sending server. Many receiving mail servers, especially those with stringent anti-spam policies, will check if the IP address from which an email originates has a corresponding PTR record. This check adds a layer of trust, as legitimate mail servers typically have properly configured PTR records, while spammers often do not.

The absence of a PTR record or a misconfiguration can significantly impact email delivery. If an rDNS lookup fails or returns an unexpected hostname, receiving servers may flag the email as suspicious, increase its spam score, or even reject it outright. For instance, properly configured PTR records improve credibility for your mail server, helping to protect against issues like being added to a blacklist (or blocklist).

Configuring a PTR record

PTR records are generally managed by the owner of the IP address, which is typically your internet service provider (ISP) or hosting provider. You usually cannot create them yourself through your domain's DNS management interface. You need to contact your provider and request them to set up or modify the PTR record for your sending IP address to resolve to your email sending domain or a relevant subdomain.

The significance of HELO/EHLO

The HELO (or EHLO for Extended HELO) command is one of the very first commands exchanged between two mail servers during the SMTP handshake process. When your mail server connects to a recipient's mail server, it identifies itself using the HELO or EHLO command, presenting a hostname. This hostname is a critical piece of information that the receiving server uses to identify your mail server.

The hostname presented in the HELO command should ideally match the PTR record of the sending IP address. This alignment creates a consistent and verifiable identity for your mail server. A mismatch between the HELO hostname and the PTR record can raise red flags with receiving servers, as it might suggest an attempt to obscure the sender's true identity, which is a common tactic used by spammers.

Receiving servers often perform a series of checks, including verifying that the HELO hostname is a fully qualified domain name (FQDN) that resolves back to the sending IP address. If this check fails, or if the HELO string looks generic (e.g., "localhost" or an IP address instead of a domain name), it can negatively impact your sender reputation and lead to messages being filtered as spam or rejected.

Impact on deliverability and reputation

Both PTR records and HELO commands significantly impact email deliverability because they contribute to the sending server's overall credibility and trust. Receiving mail servers use these DNS records as part of their anti-spam and anti-phishing measures. They are fundamental authentication checks that precede more advanced protocols like SPF, DKIM, and DMARC. If these basic checks fail, subsequent authentication steps may be ignored or viewed with increased suspicion, leading to poor inbox placement.

Major email providers, including

Google,

Microsoft (Outlook/Hotmail), and

Apple (iCloud), place varying degrees of importance on these records. While some may still deliver emails without perfect alignment, a strong and consistent sender identity across all these checks contributes positively to your domain and sender reputation. A negative reputation can impact delivery rate.

Conversely, misconfigured PTR or HELO records can lead to emails being marked as spam, sent to the junk folder, or blocked entirely. This can especially be the case for smaller ISPs or organizations with very strict email security policies. It's a common reason why your emails go to spam or get caught in a spam filter, leading to being placed on a blacklist or blocklist (DNSBLs).

Ensuring the PTR record and HELO command are properly set up provides foundational trust signals that receiving servers look for. It's not the only factor, but it's a significant one that can impact whether your email makes it past the initial gatekeepers of the inbox. This is also a crucial aspect of how email blacklists work, as inconsistent records can contribute to a server's reputation being negatively impacted and potentially listed.

Positive alignment

Trust and legitimacy: Aligns with security best practices, verifying that the sending server is authorized.
Improved deliverability: Increases the likelihood of emails reaching the inbox, avoiding spam folders.
Enhanced sender reputation: Positively contributes to your domain and IP reputation over time.

Negative impact

Increased spam scoring: Emails more likely to be flagged or sent to junk.
Email rejection: Receiving servers may outright reject emails from unverified sources.
Blocklisting risk: Higher chance of your sending IP or domain being added to a blacklist.

Best practices and alignment

To maximize your email deliverability, ensuring proper configuration and alignment of your PTR records and HELO commands is essential. Here are some key best practices:

Consistent alignment: The hostname specified in your mail server's HELO/EHLO command should match the domain name in your PTR record. Both should then ideally resolve forward to the sending IP address. This alignment is a best practice.
Use a fully qualified domain name (FQDN): Ensure your HELO/EHLO command presents an FQDN, like mail.yourdomain.com, rather than just your domain or an IP address.
Dedicated IP addresses: If you use an email service provider (ESP) with shared IP addresses, you might not have control over PTR records or HELO. For high-volume senders, a dedicated IP allows full control and better reputation management. You can learn more about how rDNS impacts deliverability with dedicated IPs.
Regular monitoring: Periodically check your PTR records and confirm your HELO command is correctly configured. Tools are available for this purpose.

Implementing these best practices helps build a stronger, more trustworthy sending reputation, ultimately improving your email deliverability rates.

Views from the trenches

Best practices

Always ensure your mail server's HELO command presents a fully qualified domain name (FQDN).

Align your HELO hostname with your PTR record for optimal authentication and trust.

For dedicated IPs, ensure your hosting provider or ISP correctly configures the PTR record.

Common pitfalls

Using a generic HELO string like 'localhost' or an IP address instead of a domain name.

Having a PTR record that does not match the HELO hostname or the sending domain.

Overlooking PTR records when setting up new mail servers or migrating IPs.

Expert tips

Even if your primary email authentications (SPF, DKIM, DMARC) are strong, foundational DNS records like PTR and HELO still contribute to overall sender reputation.

Smaller, stricter email providers are more likely to perform granular checks on PTR and HELO, so consistent configuration is vital for broad inbox placement.

If using a shared IP pool, inquire with your ESP about their PTR and HELO practices; while less customizable, they should still be optimized for deliverability.

Marketer view

Marketer from Email Geeks says the PTR record might not matter significantly for deliverability, especially when considering large providers like Google that send from generic PTRs, though this warrants further research.

2022-07-20 - Email Geeks

Marketer view

Marketer from Email Geeks says some smaller ISPs, such as T-Online, can be particular if the sending IP's PTR domain does not match the sending domain, potentially affecting deliverability.

2022-07-20 - Email Geeks

Foundational elements for email trust

PTR records and HELO commands are fundamental components of email deliverability. While often overshadowed by more complex authentication protocols, their proper configuration and alignment provide a crucial layer of trust and verification for receiving mail servers. Neglecting these basics can lead to increased spam filtering, rejections, and a damaged sender reputation.

For optimal deliverability, ensure that your sending IP has a correctly configured PTR record that resolves to a relevant domain, and that your mail server's HELO/EHLO command uses a fully qualified domain name that aligns with this PTR record. These proactive steps are vital for maintaining a healthy email sending infrastructure and ensuring your messages consistently reach their intended recipients' inboxes.