Cannot send emails to bellsouth.net or att.net.

This is the message I received.

1/12/2025 11:13:12 PM - Server at DS0PR05MB9175.namprd05.prod.outlook.com returned '550 5.4.316 Message expired, connection refused(Socket error code 10061)'
1/12/2025 11:02:54 PM - Server at bellsouth.net (144.160.159.21) returned '450 4.4.316 Connection refused [Message=Socket error code 10061] [LastAttemptedServerName=bellsouth.net] [LastAttemptedIP=144.160.159.21:25] [SmtpSecurity=-2;-2] CH3PEPF0000010C.namprd04.prod.outlook.com 2025-01-12T23:03:11.961Z 08DD32CDA0570099'

It would be helpful to have assistanced from Microsoft in determining why bellsouth.net servers refused connections from outlook.com servers. My email address is in the safe senders list for the recipients that don't receive the emails.

Vic

Dear Linda GrondahlThanks for using Microsoft products and posting in the community.Based on your description, I know you cannot receive specific emails I have contacted each person and they are receiving emails from other people - just not me. I think it's possible that these two domains have set your email as spam, causing them to be unable to receive it. Sending group emails does have a chance of being recognized as spam by the server, but once recognized by the server, you cannot send any emails, but your other friends can still receive your emails. Therefore, I suggest that you contact colleagues from those two domains and ask them to set your email as a secure contact.If you have any questions, please contact us and we will get back to you as soon as possible!Thank you for your understanding and cooperation.Best regardsKokutou-MSFT |Microsoft Community Technical Support Specialist

I need a solution in simple English

We are having the same issue with deliverability to a bellsouth.net email user from our M365 service. NDR states:

A security check at bellsouth.net failed due to misconfigured settings at <our domain>.com

Misconfigured PTR record

A test with mail-tester.com reports:

Your IP address 52.101.61.73 is associated with the domain mail-centralusazon11020073.outbound.protection.outlook.com.

Nevertheless your message appears to be sent from DM1PR04CU001.outbound.protection.outlook.com.

You may want to change your pointer (PTR type) DNS record and the host name of your server to the same value.

Here are the tested values for this check:

IP: 52.101.61.73

HELO: DM1PR04CU001.outbound.protection.outlook.com

rDNS: mail-centralusazon11020073.outbound.protection.outlook.com

Checking other Microsoft forums, this article state that it is by design (on the M365 side) and implies that recipient mail servers should NOT be using the reverse DNS test.

https://learn.microsoft.com/en-us/exchange/troubleshoot/antispam-and-protection/cannot-send-emails-to-external-recipients

All my friends who have bellsouth.net do not receive my emails. How does one fix this

This is what I get

lph835.prodigy.net rejected your message to the following email addresses:

@bellsouth.net (@bellsouth.net)Your message couldn't be delivered because the recipient's email server (outside of Office 365) rejected it because it couldn't determine if your message is coming from a location that is associated with your email domain. This is a security measure commonly done to help prevent malicious email or spam email from entering the recipient's email system. The reason the lookup failed is likely because your domain's email settings aren't set up correctly. To fix this, forward this non-delivery report (NDR) to your email admin.

For Email Admins
When Office 365 tried to send the message to the recipient's email server (outside Office 365), the external email server returned the error below. This means that when the recipient's email server was asked to accept the sender's message the server likely performed a reverse DNS (rDNS) lookup and the lookup failed. An email server outside Office 365 may perform an rDNS lookup to validate that the IP address the message is coming from is associated with your domain. The failed rDNS lookup suggests that the PTR record (pointer DNS record type) for your domain isn't set up properly.

To fix this, work with your DNS hosting provider (your domain registrar, Web hosting provider, or ISP) to set up a correct PTR record for your domain. If you're using Office 365 to manage your DNS records note that PTR record creation and management isn't supported by the Office 365 interface, in which case you'll have to change your DNS management to a DNS host outside Office 365. Refer to this article for instructions on how to do this:Change how DNS records are managed with Office 365.

Setting up PTR records is not supported by Office 365. Office 365 support will not be able to help you fix this problem.

flph835.prodigy.net gave this error:Remote server returned invalid or missing PTR (reverse DNS) record for sending domain -> 550 5.7.1 Connections not accepted from servers without a valid sender domain.flph835 Fix reverse DNS for 52.103.7.78