What do PTR and HELO records mean in relation to AT&T email blocking, and whose responsibility are they?

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.

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.

Email marketer from Valimail shares that HELO/EHLO provide the hostname of the sending server, while PTR records map an IP address to a hostname. A mismatch between the hostname presented in HELO/EHLO and the hostname associated with the IP address via PTR record can flag emails as potentially spam.

Email marketer from MXToolbox explains that reverse DNS helps map IP addresses to domain names and, therefore, is useful to diagnose mail server issues.

Email marketer from Postmark shares that reverse DNS helps ensure that the IP is associated with a domain, which helps establish its legitimacy and helps prevent spoofing.

Email marketer from DNSQueries shares that typically your ISP/Hosting provider has the responsibility for managing your DNS records. This includes PTR records.

Email marketer from Reddit explains that HELO must resolve to a valid DNS address. If your HELO is not a valid address with a PTR record, some receiving mail servers will reject the email as spam. Many ISPs and email providers use this as a basic test for legitimacy.

Email marketer from Mailhardener shares that PTR records help confirm a mail server is genuine. They are an important part of reverse DNS lookups, which mail servers use to verify identity.

Email marketer from Email Geeks believes there were some other red flags that AT&T did not want to reveal and, just shared a way how those flags could be avoided in some cases instead.

Email marketer from Sendgrid explains that the HELO/EHLO commands can affect email deliverability, especially if the hostname presented doesn't match what's expected based on DNS records.

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.

Expert from Spam Resource explains that your HELO domain is critically important, it needs to be a real domain, not a made up name.

Expert from Email Geeks states that all this is the ESP's problem.

Expert from Word to the Wise shares that reverse DNS can help build IP reputation, but it's more important to avoid negative impacts than to guarantee positive ones.

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.

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.

Documentation from RFC Editor explains that HELO/EHLO command initiates an SMTP session. The EHLO command allows the SMTP server and client to negotiate extensions to the SMTP protocol. It identifies the sending SMTP client to the SMTP server.

Documentation from Microsoft Learn explains that a PTR record, also known as a Reverse DNS record, resolves an IP address to a domain/hostname. It's used to verify that the server sending an email is authorized to use the domain it's sending from.