From: "Lewis G Rosenthal" <ecs-isp@2rosenthals.com>
Received: from [50.73.8.217] (account lgrosenthal@2rosenthals.com HELO [192.168.200.27])
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Subject: Re: [eCS-ISP] Anyone else seeing issues today with AT&T and RDNS
 failures when sending?
To: eCS ISP Mailing List <ecs-isp@2rosenthals.com>
References: <list-12280221@2rosenthals.com> <list-12280249@2rosenthals.com>
Organization: Rosenthal & Rosenthal, LLC
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Date: Thu, 20 Feb 2025 16:03:12 -0500
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On 02/20/25 03:56 pm, Paul Smedley wrote:
> Hey Lewis,
>
> On 21/2/25 07:05, Lewis G Rosenthal wrote:
>> Hi, all...
>>
>> It's rare that I get an RDNS failure for one of my server IPs, as I know 
>> I have (and have just confirmed again) valid RDNS records in my 
>> providers' DNS.
>>
>> Today, att.net rejected mail from us to one of their subscribers with a 
>> 550 5.7.1 error:
>>
>>   <recipient-address @ att.net>
>>     host ff-ip4-mx-vip1.prodigy.net [144.160.159.21]
>>     SMTP error from remote mail server after MAIL FROM:<sender from the 
>> 2rosenthals.com domain>:
>>     550 5.7.1 Connections not accepted from servers without a valid 
>> sender domain.flph829 Fix reverse DNS for 50.73.8.217
>>
>>
>> 50.73.8.217 is our Leesburg, VA public IP on Comcast's network (I know; 
>> I'm so ashamed...we're in the only four square blocks in downtown 
>> Leesburg where Verizon FiOS is *still* not available). The RDNS record is:
>>
>> secmgr-va.2rosenthals.com
>>
>> (verified a few minutes ago at MX-Toolbox)
>>
>> I'm wondering if anyone else is having difficulty today.
>>
> Confirmed also that rdns works for your IP from the other side of the 
> planet..
>
> psmedley@ThinkPad-X13-Gen-1:~$ host 50.73.8.217
> 217.8.73.50.in-addr.arpa domain name pointer secmgr-va.2rosenthals.com.
>

Thanks, Paul.

I'm thinking that we hit a brain-dead AT&T server which couldn't get a 
reasonable response from its own configured DNS server. As we know, the 
5.7.1 error only really means that the server checking could not get the 
data. It doesn't tell us why. I told Craig to try again in a few minutes.

Big ISPs...gotta love 'em.

-- 
Lewis
-------------------------------------------------------------
Lewis G Rosenthal, CNA, CLP, CLE, CWTS, EA
Rosenthal & Rosenthal, LLC                www.2rosenthals.com
visit my IT blog                www.2rosenthals.net/wordpress
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