What do PTR and HELO records mean in relation to AT&T email blocking, and whose responsibility are they?
Matthew Whittaker
Co-founder & CTO, Suped
Published 26 Apr 2025
Updated 18 Aug 2025
6 min read
Dealing with email blocking can be incredibly frustrating, especially when it comes from major mailbox providers like AT&T. I've seen many clients struggle with cryptic bounce messages or vague explanations from postmasters. One common scenario involves mentions of PTR and HELO records. These terms often sound like technical jargon, but understanding them is crucial for ensuring your emails reach their intended recipients.
I recently had a client who was experiencing blocks from AT&T, and despite their Email Service Provider (ESP) confirming that reverse DNS was in place, AT&T's response was still confusing. They hinted at differences between shared MTAs and dedicated MTAs in relation to PTR and HELO alignment. This highlights a common point of confusion for many senders.
So, what exactly do PTR and HELO records mean, especially when AT&T is involved in blocking your emails? And, perhaps more importantly, whose job is it to make sure these are set up correctly? Let's dive into these often misunderstood aspects of email deliverability.
Understanding PTR records
A PTR record, also known as a Pointer Record or Reverse DNS record, performs the opposite function of a standard A record. While an A record maps a domain name to an IP address, a PTR record maps an IP address back to a domain name (or hostname). It's a fundamental part of the internet's Domain Name System (DNS).
For email, PTR records are critical for reputation and anti-spam measures. When your mail server sends an email, the recipient's server often performs a reverse DNS lookup. This means it takes the sending IP address and queries the DNS to see if there's a PTR record that points back to a legitimate hostname. This helps verify that the sender is who they claim to be, acting as a basic authentication step.
Example PTR record
192.0.2.10.in-addr.arpa. IN PTR mail.yourdomain.com.
Many email providers, including AT&T, extensively use PTR records in their filtering processes. If a sending IP address lacks a valid PTR record, or if the record is misconfigured, it can raise a red flag. This often leads to reverse DNS failure bounces or outright blocking, as the mail server might suspect the incoming email is spam or malicious. You can learn more about understanding PTR DNS records for emailing.
The importance of PTR records
A PTR record is a vital signal of legitimacy for your email sending infrastructure. Without it, or with an incorrect one, your emails are far more likely to be flagged as suspicious and land in the spam folder, or even be rejected entirely by recipient servers.
Deciphering HELO/EHLO
HELO (or EHLO, the Extended HELO) is one of the first commands exchanged between sending and receiving mail servers during an SMTP (Simple Mail Transfer Protocol) session. When your mail server connects to the recipient's server, it introduces itself with a HELO or EHLO command, typically followed by its hostname, for example, HELO mail.yourdomain.com. This command announces the sender's identity to the receiver.
The critical part for deliverability is the relationship between this HELO hostname and the PTR record. Recipient mail servers expect consistency. They want to see that the hostname your server announces in its HELO command matches the hostname returned by a reverse DNS lookup of your sending IP address. This is known as PTR and HELO alignment.
Shared MTAs (Mail Transfer Agents)
When you send emails through a large ESP, you often use shared MTAs where many different clients send from the same pool of IP addresses. In this scenario, it's common for the PTR record of the sending IP to point to a generic hostname controlled by the ESP. The HELO hostname might also be generic or related to the ESP's infrastructure. ISPs like Google and AT&T generally understand this setup for shared IPs, as long as the PTR is valid and consistent with the HELO, even if it doesn't directly mention your specific domain.
Dedicated MTAs (Mail Transfer Agents)
If you have dedicated IP addresses for your email sending, AT&T and other providers often expect a stricter alignment. In this case, they prefer that the PTR record for your dedicated IP address matches the hostname your server introduces itself with in the HELO command. This provides a stronger signal of trust and legitimate sending behavior for high-volume or critical email streams.
The significance of PTR and HELO alignment for AT&T
The primary reason AT&T, and indeed most major mailbox providers, care so much about PTR and HELO alignment is for spam and fraud prevention. A properly configured PTR record that aligns with the HELO hostname indicates a legitimate mail server. Conversely, a mismatch or missing record is a common characteristic of spamming operations or compromised systems.
When an IP address is on an email blocklist (also known as a blacklist), it's often due to these underlying trust signals being absent or incorrectly configured, combined with other factors like sending to spam traps or high complaint rates. AT&T's systems are designed to be quite sensitive to these indicators.
DNS Record
Function for email
Why it matters
A record
Maps a domain to an IP address.
Essential for recipients to find your mail server's IP.
MX record
Specifies mail servers responsible for receiving email for a domain.
Directs incoming email to the correct server.
PTR record
Maps an IP address back to a hostname (reverse DNS).
Used by receiving servers to verify the sending IP's identity, crucial for anti-spam.
HELO/EHLO
The hostname a sending server announces to a receiving server.
Expected to align with the PTR record for authenticity.
When AT&T or other providers report a reverse DNS failure it means one of these aspects is off. Either the PTR record is missing, incorrectly configured, or doesn't match the HELO hostname. This inconsistency is a major reason why emails get blocked or flagged as spam, directly impacting your email deliverability.
Whose responsibility are they?
For most businesses and marketers, PTR and HELO record management falls squarely on the shoulders of their Email Service Provider (ESP). When you sign up with an ESP to send your marketing, transactional, or bulk emails, they provide the infrastructure, including the IP addresses your emails will be sent from. They are responsible for ensuring these IPs have correct PTR records and that their mail servers' HELO commands are properly aligned.
If you're self-hosting your email, or if your organization manages its own mail servers, then the responsibility for PTR and HELO setup, as well as their alignment, rests with your IT or network administration team. It's a critical aspect of setting up a robust and deliverable email sending infrastructure. In either case, if you encounter AT&T blocking, your first step should be to engage with whoever manages your sending infrastructure to investigate the PTR and HELO configuration.
ESP responsibility
If AT&T (or any other provider) flags your emails due to PTR or HELO issues, and you use an ESP, it is their responsibility to address these technical configurations. They should have the expertise and control over the sending IPs to correct any misalignments. Don't hesitate to contact your ESP's support team with the bounce message or the details provided by AT&T. You may also need to contact the AT&T postmaster to get clarity on the specific blocking reason.
Views from the trenches
Best practices
Ensure PTR records for your sending IPs resolve to a legitimate, publicly accessible hostname.
Verify that your HELO/EHLO hostname matches the PTR record's hostname for dedicated IPs.
Regularly monitor your email deliverability and bounce logs for reverse DNS failures.
Communicate proactively with your ESP about any deliverability issues reported by ISPs.
Implement DMARC, DKIM, and SPF alongside PTR and HELO for comprehensive email authentication.
Common pitfalls
Assuming PTR is automatically correct when setting up new sending infrastructure or IPs.
Ignoring bounce messages that cite reverse DNS or HELO mismatches, leading to ongoing blocking.
Not understanding the difference in requirements for shared vs. dedicated IP pools.
Attempting to manage complex DNS records without sufficient technical expertise.
Failing to follow up with ESPs or postmasters when issues are reported.
Expert tips
Check your PTR record setup using online DNS lookup tools or command-line utilities like 'dig -x <IP_ADDRESS>'.
If using an ESP, confirm their best practices for PTR and HELO alignment.
For dedicated IPs, choose a HELO hostname that is descriptive and reflects your sending domain, e.g., 'mta.yourdomain.com'.
Understand that even if a block is removed, underlying misconfigurations can lead to future issues.
Remember that PTR and HELO are foundational, but comprehensive authentication includes SPF, DKIM, and DMARC.
Expert view
Expert from Email Geeks says a PTR record states that a given IP is a specific hostname, and HELO is the initial SMTP transaction where the sending MTA introduces itself with a server name. AT&T is indicating that the hostname in the PTR record is different from how the machine is identifying itself, and this is typically the ESP's responsibility.
2024-01-30 - Email Geeks
Marketer view
Marketer from Email Geeks says they suspected the ESP was responsible for fixing the issue and now knows who to contact next for resolution.
2024-01-30 - Email Geeks
Maintaining email deliverability
Understanding PTR and HELO records, and their expected alignment, is fundamental to successful email deliverability. Especially when dealing with strict filtering policies from providers like AT&T, these DNS configurations are not just technical formalities, they are core trust signals. A misconfigured or misaligned setup can lead directly to your emails being blacklisted or blocked.
For the vast majority of email senders, ensuring these records are correct falls to your Email Service Provider. If you're encountering blocking issues with AT&T or any other mailbox provider, specifically related to reverse DNS or HELO, consult with your ESP. They are equipped to diagnose and resolve these technical aspects of your sending infrastructure.
Maintaining proper PTR and HELO configuration, alongside other authentication standards like SPF, DKIM, and DMARC, is an ongoing process that significantly contributes to your email program's success. It helps establish your legitimacy as a sender and improves your overall inbox placement.
AT&T. I've seen many clients struggle with cryptic bounce messages or vague explanations from postmasters. One common scenario involves mentions of PTR and HELO records. These terms often sound like technical jargon, but understanding them is crucial for ensuring your emails reach their intended recipients.
Google and AT&T generally understand this setup for shared IPs, as long as the PTR is valid and consistent with the HELO, even if it doesn't directly mention your specific domain.
