What are PTR records and are they essential for email deliverability, along with other DNS records like A and MX?

Key findings

• PTR records: These are crucial for reverse DNS lookups, mapping an IP address back to a hostname. They are a fundamental layer of trust, verifying that the IP sending the email is indeed associated with the domain it claims to be from. Many receiving mail servers perform this check as a critical anti-spam measure.
• A records: These perform the forward DNS lookup, translating a domain name into an IP address. While a primary domain needs an A record for website accessibility, its direct relevance for email sending (especially for return-path domains) is debated, with some experts considering it less critical than MX records.
• MX records: These specify which mail server is responsible for receiving emails for a domain. They are absolutely essential for inbound email delivery and are also a strong signal of a legitimate domain for outbound mail, particularly for return-path domains.
• FCrDNS (Forward-Confirmed Reverse DNS): This refers to a state where both the forward DNS lookup (A record) and the reverse DNS lookup (PTR record) for a given IP address and hostname match. Achieving FCrDNS strengthens sender credibility and is a preferred configuration for many mailbox providers to ensure robust email authentication.
• Obligatory nature: While not all DNS records are strictly obligatory in a technical sense, the absence of properly configured PTR and MX records significantly harms email deliverability, often leading to emails being rejected or sent to spam folders. Most modern email systems expect these records to be in place.

Key considerations

• Impact on sender reputation: A complete and consistent DNS setup, including a valid PTR record, is a strong positive signal to receiving mail servers, directly influencing your sender reputation.
• Management of PTR records: Unlike A and MX records which you typically manage within your domain's DNS, PTR records for your sending IP addresses are usually configured by your internet service provider (ISP) or email service provider (ESP), as they control the IP address space.
• Return-path domain configuration: Ensuring your return-path domain (or bounce domain) has a correctly configured MX record is more critical than an A record for preventing delivery issues related to bounces.
• Troubleshooting: Misconfigured DNS records are a common cause of email delivery failures. Regularly checking your DNS setup, including PTR, A, and MX records, is a key part of maintaining good deliverability.

Key opinions

• PTR is vital: There is broad agreement that PTR records are essential for sending IPs to facilitate reverse DNS lookups, which email servers commonly use for authentication.
• MX is non-negotiable: MX records are consistently highlighted as a must-have for return-path domains, far outweighing the importance of A records for this specific purpose.
• A record debate: While A records define forward lookups, their necessity for return-path domains specifically for email deliverability is debated. Some believe a matching A record contributes to a complete DNS cycle (FCrDNS), which can prevent issues with some blacklists, while others argue it's not a critical factor for ISPs.
• FCrDNS benefits: Even if not universally enforced, a full Forward-Confirmed Reverse DNS (FCrDNS) cycle is seen as a logical best practice that can avoid being flagged by stricter anti-spam systems.
• Industry practice varies: Observations of major ESPs show a mix of practices regarding A records for return-path domains, indicating that it's not a universally adopted standard, though many still implement it.

Key considerations

• Avoiding blocklists: Some smaller blocklists (or blacklists), like SPFBL, may flag domains without a full FCrDNS cycle, making complete DNS setup a preventative measure against such listings.
• Legacy vs. new infrastructure: Newer email sending infrastructure often includes A records as part of the setup, even if older systems do not, suggesting an evolving best practice.
• Return-path domain reputation: While A records for return-path domains might not always be checked by major ISPs, having a proper MX record for bounce handling is essential for maintaining the reputation of that domain. For more on this, check our guide on why email validation services flag domains without MX records.
• Beyond deliverability: Some A records serve purposes unrelated to SMTP, such as redirecting hostnames to a corporate website, which is a good practice for overall domain presence but doesn't directly impact email.

Key opinions

• PTR is fundamental for trust: Experts universally agree that PTR records are a baseline requirement for legitimate email sending. Without them, emails are highly likely to be flagged as spam or rejected, as reverse DNS checks are standard practice for receiving servers.
• FCrDNS is a strong signal: Achieving Forward-Confirmed Reverse DNS (matching A and PTR records) provides a robust authentication signal, making it harder for spammers to impersonate legitimate senders. This consistency is highly valued by ISPs.
• MX record criticality: MX records are deemed absolutely critical for any domain involved in email, especially the return-path domain, as they dictate where bounces and other mail server communications should be sent. Their absence implies a lack of proper mail handling.
• A records for return path: While an A record is generally required for a domain to resolve, its direct necessity for a return-path domain (separate from MX) is often seen as less vital by experts, though some small blacklists might still check for it.
• Consistency is key: The overall consistency across all DNS records (PTR, A, MX, SPF, DKIM, DMARC) for a sending domain is what truly builds sender reputation and ensures successful delivery.

Key considerations

• Default filtering: Mail servers may apply default filters or even reject emails from IPs that lack proper PTR records, treating them as suspicious or unverified.
• Delegation to ESPs: For many senders, leveraging their ESPs (Email Service Providers) to manage PTR records and other sending domain DNS is the most reliable way to ensure correct configuration and alignment with best practices. Read about best practices for ESPs regarding HELO, rDNS, and SPF.
• Reputation impact: A misconfigured or absent PTR record can negatively impact domain reputation and increase the likelihood of emails landing in the spam folder, even if other authentication records are present. This also ties into how your Google Postmaster Tools Domain Reputation is affected.
• Beyond basic compliance: While RFCs set minimum standards, the evolving landscape of anti-spam measures means that going beyond basic compliance and aiming for optimal DNS configurations (like FCrDNS) is advisable for consistent inbox placement.

Key findings

• PTR record function: Documentation defines PTR records as being used for reverse DNS lookups, translating an IP address into a domain name. This is the inverse of what an A record does.
• A record function: A records (Address records) map a hostname to an IPv4 address, allowing computers to find web servers and other internet resources by name.
• MX record function: MX (Mail Exchange) records specify the mail servers that accept email for a domain and where those emails should be routed.
• Role in email validation: PTR records are specifically mentioned as being used by email servers to verify the authenticity of the sending host's domain name, forming a critical part of initial connection checks.
• Essential for email servers: For email servers, properly configured PTR records are considered essential for improving deliverability, logging, and overall security posture.

Key considerations

• Reverse lookup requirement: Documentation often implies that a successful reverse DNS lookup (via PTR) is expected by many mail servers, contributing to anti-spam efforts.
• Interplay of records: The various DNS records work in conjunction. For instance, SPF records rely on DNS lookups, including A records, to validate sending sources. Learn more about how SPF 'a' records affect DNS lookups.
• Security implications: PTR records are described as a security measure, helping to verify sender authenticity and combat spam and phishing attempts.
• Configuration responsibility: While A and MX records are typically managed by the domain owner, PTR record configuration often falls to the entity controlling the IP address block, such as an ISP or hosting provider.