Server at mx1.mxge.comcast.net (2001:558:fd01:2bad::5) returned '421 4.4.2 Connection dropped due to SocketError'

When looking at some support articles online for this issue, it would seem a ticket needs to be opened for the Microsoft 365 email address or the TLS settings need to be updated within the Microsoft 365’s email settings @steved13.

For troubleshooting purposes, are any of the Comcast email addresses that are not receiving the emails sent by the Microsoft 365 account, Comcast email addresses that are yours?

We can definitely troubleshoot issues with not receiving the emails if you have access to any of the impacted Comcast email addresses. Although, this issue appears to require assistance from Microsoft 365 based on the support articles I am seeing for the error messages you are receiving.

I've run the test for our server here: https://testconnectivity.microsoft.com/tests/O365ExchangeDns/input and it passes with flying colors. We don't have any issues with DKIM, SPF or DMARC. Everything has been tripled checked this AM. The office is sending to a total of SIX Comcast.net email addresses in the weekly email. This is how they have been doing it for years. There are other recipients in this email as well. I can see how it might be possibly viewed as SPAM but in this case it is rejected by the Comcast/Xfinity server altogether. If you can get this working we would all greatly appreciate it. Otherwise we will just have to tell parishioners that we cannot send email to them if they have a Comcast.net address. Thank you. 

Hi, @gjames50. I appreciate you circling back. I understand you've had some trouble as well. I see @XfinityAlex provided some feedback, and they are certainly an expert in this area. I see they are checking on this further and I would allow them more time to give you any information they find. You can also visit this link https://spa.xfinity.com/postmaster?faq=avoid-blocks-ipv4 for further assistance. 

@gjames50 Send me a DM with the domain of the sending messages.  This shouldn't still be happening.  Thanks

@gjames50 Thank you for confirming the issue is still ongoing. At this time I would recommend contacting our Xfinity Customer Security Assurance team, they would be the best team to assist you with finding a resolution. You can contact them by calling 1-888-565-4329, they are available from 8 AM - 12 AM EST, 7 days a week.

@gjames50​ Our domain also experiencing this, and it appears to have started in the last two months. We are using O365 for our organization and emails to only @comcast.net accounts bounce back. Looks to be exactly the same issue, eager to understand what the problem is.

2/8/2024 5:35:18 PM - Server at <REDACTED>.namprd12.prod.outlook.com returned '550 5.4.300 Message expired -> 421 4.4.2 Connection dropped due to SocketError'
2/8/2024 5:20:40 PM - Server at mx1.mxge.comcast.net (2001:558:fd00:4f::4) returned '421 4.4.2 Connection dropped due to SocketError'

@XfinityBillie​ I just called this number. The support technician said that sending to @comcast.net accounts requires them to be individually enumerated on emails now (no longer able to have them as part of a group). 

That seems like a somewhat daft policy...

Hello @Bargainville! I'd be happy to look further into this issue for you. Please send us a direct message with your first/last name and full address. You can start by clicking the "direct message" icon on the upper right page of the forum page. Once you click on that, input our shared handle "Xfinity Support" to send us a direct message. If you're signed in to your forums profile and because you have already posted to the public page, you should have the option to do so.