Why am I seeing reverse DNS failure bounces from ATT?
Summary
What email marketers say12Marketer opinions
Email marketer from Email Geeks indicates that the issue might be isolated to three specific nodes: <http://250-flph824.prodigy.net|250-flph824.prodigy.net>, <http://250-alph763.prodigy.net|250-alph763.prodigy.net>, and <http://250-alph753.prodigy.net|250-alph753.prodigy.net>.
Email marketer from Sendgrid responds that reverse DNS records are necessary to prove that your sending IP has permission to send using your sending domain. If ATT isn't sure if your IP has permission, they will reject it.
Email marketer from SocketLabs responds that a common issue could stem from a mismatch between your sending server's hostname and what's listed in your rDNS record. This mismatch can be a red flag for ATT, leading to bounced emails.
Email marketer from EasyDMARC shares that another possibility is that AT&T's systems might be temporarily experiencing issues. While less common, occasional glitches on their end can cause transient reverse DNS lookup failures.
Email marketer from Mailjet Blog highlights that shared IP addresses can sometimes be blacklisted, causing reverse DNS lookup failures even if your own configuration is correct. They recommend checking if the IP is on any blacklists.
Email marketer from Reddit shares that ATT is very strict with reverse DNS. They state if your IP address doesn't have a proper PTR record pointing to your sending domain, ATT will likely reject your emails.
Email marketer from Postmastery Blog answers that AT&T's systems are designed to reject mail from any server lacking a properly configured and verifiable rDNS record. This is due to it assisting them to reduce spam. Also, some email-sending services often don't set up rDNS records on customers' behalf.
Email marketer from EmailForum.org explains that a common cause is a recent IP address change. If you've just switched servers or IPs, it can take some time for the reverse DNS record to propagate across the internet. During this period, ATT may reject emails.
Email marketer from Gmass answers to contact your Internet Service Provider (ISP) or hosting provider to set up a reverse DNS record for your sending IP address. They are the ones who control the DNS records associated with your IP block.
Email marketer from Email Geeks reports seeing about 10% failure rate with the error message: smtp;550 5.7.1 Connections not accepted from servers without a valid sender domain.flph824 Fix reverse DNS for 52.124.3.112
Email marketer from StackExchange suggests checking the PTR record using online tools. They indicate if the tool shows no PTR record or a record that doesn't match your sending domain, that is likely the reason for the bounces from ATT.
Email marketer from Email Geeks shares that this issue has been reported to AT&T multiple times and confirms it was resolved yesterday evening.
What the experts say5Expert opinions
Expert from Word to the Wise responds that it is imperative to make sure that your reverse DNS is properly set up and matches forward records to avoid getting rejected by ATT.
Expert from Spam Resource explains that many systems check that every mail-sending IP address has a PTR record. AT&T and other ISPs often block mail without reverse DNS, so missing PTR will cause failures.
Expert from Email Geeks shares that as of their last test send at 8:30 am, they are not seeing reverse DNS failure bounces from ATT addresses.
Expert from Email Geeks explains that typically FP DNS failures are localized to a single ESP or even part of an ESP and recommends reaching out to ATT.
Expert from Word to the Wise emphasizes that reverse DNS is part of email reputation. ISPs like AT&T use this as a signal to decide whether to accept or reject mail. A mismatch, or an absence of it, will contribute to deliverability problems.
What the documentation says5Technical articles
Documentation from Microsoft Learn explains that a reverse DNS lookup, or PTR record, resolves an IP address to a domain name. A failure indicates that the IP address being used doesn't have a corresponding PTR record, or the record isn't correctly configured, which can lead to email delivery issues with providers like ATT.
Documentation from Digital Ocean responds that to have the forward DNS entry and the reverse DNS entry point to the same domain, there are requirements. Usually it is that an A record needs to exist before the PTR can be setup. Check with your ISP if you are unsure of requirements.
Documentation from RFC answers explains that reverse DNS entries are stored in a special domain called IN-ADDR.ARPA. If the sending mail server's rDNS records don't match this requirement, they might be blocked.
Documentation from SparkPost Support explains that a missing or misconfigured reverse DNS (rDNS) record can cause email rejections. ATT, like many ISPs, uses rDNS to verify the authenticity of sending servers. Failure indicates ATT can't validate the sending server's domain, leading to bounces.
Documentation from Google Workspace Admin Help emphasizes the importance of a matching forward and reverse DNS record. If the IP address resolves to a domain, and that domain resolves back to the same IP, it strengthens sender reputation. Failure to have this match can trigger filters at ISPs like ATT.