Emails not received to Comcast addresses in mass distro list

I am having issues receiving certain emails too.  This started the beginning of the month/year.  I receive some emails but not all especially from a mass distribution sender.  Also cannot receive emails from my bank when trying to complete multi layer authentication to access account.  I've always received them previously.  Called Comcast today but after 1 1/2 hours of frustration all they did was have me sign out totally from my Xfinity account and it didn't help.  I heard from a personal friend that she was not receiving any emails to her comcast account either.  Anyone else having this issue?

Yes! I am having this exact same problem with mass emails I send for my committee. All the receivers that are @comcast.net are not receiving due to that same Throttle error message. I tried reducing the number of emails sent to 15 and still having the issue. My tech tried slowing down the send rate, but it did not help for these comcast emails. This just started happening recently. Help!!!!

I am having the same issue. I have a mass distribution list (less than thirty names) for my work and on three occasions only recipients with comcast emails are being bounced though I do not get notified until days later. Even adding myself to the list with my personal comcast account had the same result. The error is:

Your message couldn't be delivered. Despite repeated attempts to contact the recipient's email system it didn't respond.

Contact the recipient by some other means (by phone, for example) and ask them to tell their email admin that it appears that their email system isn't accepting connection requests from your email system. Give them the error details shown below. It's likely that the recipient's email admin is the only one who can fix this problem.

For more information and tips to fix this issue see this article: https://go.microsoft.com/fwlink/?LinkId=389361.

@johnho3636

Hello this link https://www.xfinity.com/support/articles/spam-filters-and-email-blocking-new-experience has great information on checking your spam filers  as well as this link for sending to xfinity  

https://spa.xfinity.com/postmaster?faq=avoid-blocks-ipv4

I posted in a forum with an issue and was hoping a Comcast monitored these and offered help. Does this happen? Can an employee respond here and can I point you to my original post that I and a lot of other email users need help with?

To the Support staff at Comcast/Xfinity, this is not a spam filter issue. I don’t think you understand what our issues are. All of a sudden, we have stopped receiving emails sent by small or large companies/businesses or individuals. They are apparently being blocked by Xfinity to our email Inboxes. We need technical assistance with this issue immediately.

... 1/23/2024, 11:10 AM | Defer | Reason: [{LED=451 4.2.0 Throttled ...

You need help from a grownup. Let's see if @XfinityAlex has a minute or two to spare . . .

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

@johnho3636 Could you share the sending domain or IP address? The domain is more relevant here, but either could help.

This is happening to multiple people and businesses in the past month… not to one person or domain… it is Comcast that has the issue. In my case my domain is CranberryCatholic.org. And the issue is distribution list being blocked or timing out at Comcast end. Individual emails go out okay.

Adding my domain as a comment in case XFinityAlex doesn't see the reply!

boyertownasd.org

I have been managing email servers for a few organizations over the last 20 years.  I find it hard to believe that so many people sending to comcast.net recipients have their own email servers configured incorrectly.  The mass public did not suddenly enter bad settings onto their email servers to cause email only to comcast.net to not be delivered correctly.  Comcast recently changed something with their email processing - not the rest of the world.  However, the sampling of the mass public having this issue could all be doing the same thing - sending out mass emails.  The users in this thread are churches, non-profits, school districts, and others whose mass email recipients are going to be large lists of personal email addresses, not work email addresses, so there will be lots of comcast.net destinations in the email blasts.

My example below is for a bounce that went to 32 comcast.net recipients.  The number of recipients may be the issue.  A possible workaround is to instead send to smaller chunks of recipients, see if using BCC will get emails through, or use products designed for mass emails, such as SalesForce.com or ConstantContact.

@XfinityAlex - are you able to disclose exactly what change you made a day or two ago, or at least the nature of the change, that you believe may have helped?

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For those using MS365 to send email, bounce messages look like this:

(One of these appears in the NDR for each recipient.)

Later in the email is a compilation of diagnostics that administrators look at to determine the cause.  It is apparent that the root cause is on Comcast's end.  However, with Comcast not yet telling us why this is happening (such as too many recipients) the blame could be on the sender.  

We at aldersgatede.org are having the same issue.  The e-mails we send to @comcast.net addresses are failing with the same error.  This has been going on since early December 2023.

I am having this same issue at...aldersgatede.org.  Whenever we send a group email, nothing goes through to any of the @comcast.net emails although other e-mail services receive and process the email just fine.  I sent a long time on the phonetoday  trying to find someone in Comcast to help me with this  only to be told to report the issue via spa.xfinity.com (again).  I'm sure hoping Alex can help us!!!

@XfinityAlex 

PLEASE HELP!

My company is suddently having this same exact issue when trying to send a weekly volunteer email! The email gets sent/delivered fine to all recipients EXCEPT the comcast.net email addresses (~30 or so in the list).

ERROR: https://postmaster.comcast.net/#RL000010};[{LED=451 4.2.0 Throttled - 

Our MSP is zero help and we don't know where else to turn to get this fixed! 

communityfoodshare.org

This is so frustrating and I do NOT want to spend one minute of my precious time on the phone with some support person that is not going to have a clue what I am talking about (I treasure what few brain cells I have left)!

THANK YOU!!!!

@XfinityAlex can you please help me as well. I've been dealing with this for months and have called into the assurance team multiple times but can't get any help. Our company is having the same issue as everyone above, our domain is genecooksupports.org 

Can you please help? 

This is the message we get, the e-mails get throttled then eventually time out. It happens anyone that sends from genecooksupports.org to an @comcast user.

Reason: [{LED=451 4.2.0 Throttled - https://postmaster.comcast.net/smtp-error-codes.php#RL000010};{MSG=};{FQDN=2001:558:fd02:243f::3};{IP=2001:558:fd02:243f::3};{LRT=1/31/2024 2:26:16 PM}]. OutboundProxyTargetIP: 2001:558:fd02:243f::3.