When sending email messages to the various AT&T consumer email domains (ameritech.net, att.net, bellsouth.net, currently.com, flash.net, nvbell.net, pacbell.net, prodigy.net, sbcglobal.net, snet.net, swbell.net, wans.net, worldnet.att.net) recently, you might have run into intermittent SMTP delays or rejections that had error messages looking something like this:
451 4.1.8 Client IP address x.x.x.x does not resolve. flpd569. Fix reverse DNS. For more information email postmaster@prodigy.net.
550 5.7.1 Connections not accepted from servers without a valid sender domain. flph830 Fix reverse DNS for x.x.x.x
550 5.7.1 Connections not accepted from servers without a valid sender domain. flph839 Fix reverse DNS for x.x.x.x
550 5.7.364 Remote server returned invalid or missing PTR (reverse DNS) record for sending domain
Is it me, or is it them?
When this issue occurs, the mailbox provider (in this case, AT&T) is telling you that it’s having trouble resolving the DNS for your email sending domain. “Connections not accepted from servers without a valid sender domain” meaning it’s having trouble resolving DNS entries under the domain name of either you or your sending platform, depending on how things are configured. In the case of reverse DNS, they’re saying that they’re not able to take the IP address of the server connecting to them and resolve it to a specific hostname in DNS under either the platform’s domain or your domain, again, depending on how it’s all configured.
When this happens, you’ll want to check to see that the various DNS entries in place for your email marketing sends are all resolving correctly. Back in my Marketing Cloud days, there were a dozen plus different DNS entries for most enterprise customers, including a customized hostname and reverse DNS for the sending IP address. (You can use my Wombatmail tool to look up the A, PTR, and other records to see if they seem to resolve properly when checked.)
It never hurts to take a cursory glance to make sure that DNS is configured correctly – be sure to fix any issues that you find.. However, when you see these kind of errors, it could be actually due to an infrastructure issue at the receiving mailbox provider – meaning, you’re not doing anything wrong. You don’t really have a DNS failure – for whatever reason, the receiving provider, in this case AT&T, is having trouble resolving legitimate DNS entries.
Ask Around
And when this happens, it’s not usually just you. Indeed, just a few days ago such an issue occurred and many senders reported seeing these issues when sending mail to the various AT&T domains. What did they have to do about it? Absolutely nothing – the issue was not theirs to fix. Thankfully, AT&T did indeed eventually resolve the issue and afterward, mail started flowing again properly.
When in doubt, check with your sending platform – or if you work for the sending platform or a large enterprise company (or are otherwise savvy enough to make the journey), posting to the Mailop list is a good way to share what you’re seeing and hear feedback from other mail administrators, email senders and email receivers, to understand if the issue is affecting you (only) or if it is more broad.
Though there really wasn’t some action here for senders to take to address the issue, I wanted to share this info so that if you run into this issue in the future, you know what to do, or not to do.
Example SMTP Errors
Is it me, or is it them?
When this issue occurs, the mailbox provider (in this case, AT&T) is telling you that it’s having trouble resolving the DNS for your email sending domain. “Connections not accepted from servers without a valid sender domain” meaning it’s having trouble resolving DNS entries under the domain name of either you or your sending platform, depending on how things are configured. In the case of reverse DNS, they’re saying that they’re not able to take the IP address of the server connecting to them and resolve it to a specific hostname in DNS under either the platform’s domain or your domain, again, depending on how it’s all configured.When this happens, you’ll want to check to see that the various DNS entries in place for your email marketing sends are all resolving correctly. Back in my Marketing Cloud days, there were a dozen plus different DNS entries for most enterprise customers, including a customized hostname and reverse DNS for the sending IP address. (You can use my Wombatmail tool to look up the A, PTR, and other records to see if they seem to resolve properly when checked.)
It never hurts to take a cursory glance to make sure that DNS is configured correctly – be sure to fix any issues that you find.. However, when you see these kind of errors, it could be actually due to an infrastructure issue at the receiving mailbox provider – meaning, you’re not doing anything wrong. You don’t really have a DNS failure – for whatever reason, the receiving provider, in this case AT&T, is having trouble resolving legitimate DNS entries.
Ask Around
When in doubt, check with your sending platform – or if you work for the sending platform or a large enterprise company (or are otherwise savvy enough to make the journey), posting to the Mailop list is a good way to share what you’re seeing and hear feedback from other mail administrators, email senders and email receivers, to understand if the issue is affecting you (only) or if it is more broad.
Though there really wasn’t some action here for senders to take to address the issue, I wanted to share this info so that if you run into this issue in the future, you know what to do, or not to do.
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