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Hulteen
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Monday, March 9th, 2026 4:25 PM

Throttled email error code 451 4.2.0

I use comcast email for my business and personal needs.  My clients are getting bounced back or delivery incomplete messages with the error code 451 4.2.0 Throttled -  https://postmaster.comcast.net/smtp-error-codes.php#RL000010

These clients have email me previously without any issues, and they are not sending large files or links.

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3 hours ago

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user_xo8tid

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2 Messages

2 days ago

Having the same issue, hopefully being worked on

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user_4r8lwi

Visitor

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3 Messages

2 days ago

YES is a big problem.   All of my emails to our accountant are being returned.  

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user_w5lbbn

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1 Message

1 day ago

Just heard from a friend who got the same error message. Comcast/Xfinity e-mail has been pretty wonky over the past week. Over several hours last week, Xfinity kept restoring to my inbox e-mails that I had deleted (and emptied my trash) in MacOS Mail.

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XfinityJamesC

Official Employee

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2.8K Messages

7 hours ago

Greetings, @Hulteen! I hope your week has been treating you well. Thanks so much for taking a moment out of your busy day to leave a post on our community forum. I'm sorry to hear you're having issues with your email, but you have definitely come to the right place for assistance.

 

How long ago did this start happening? Are the delivery errors occurring with emails from a specific domain or IP address, or are they coming from multiple sources? Do you have other emails coming in, or is everything getting bounced?

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Hulteen

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3 Messages

This started happening last week, but I don't know the specific date.  A number of my clients started reaching out that their emails to me were bounced back, reporting the Throttled error message.  This is coming from a couple of different clients, and their various emails.  Some emails are coming through, some are not.  I am unable to determine all the ones I am not getting ~ only the ones where the client mentions to me that they are having trouble. 

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4 hours ago

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XfinityRaf

Official Employee

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1.2K Messages

Thanks for those details. To confirm, have you had any issues sending emails out from that email account? 

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Please, mark a reply as the Accepted Answer.tick

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4 hours ago

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Hulteen

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No, I have not had issues sending emails.  

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4 hours ago

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XfinityRaf

Official Employee

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1.2K Messages

I appreciate you confirming that for me. If you could send our team a direct message with your full name and full address, we can take a closer look at your account, and work on getting that error message cleared. 
 

To send a "Direct Message" ("Private") message:

• Click "Sign In" if necessary

• Click the "Direct Message chat" icon

• Click the "New message" (pencil and paper) icon

• Type "Xfinity Support" in the "To:" line and select "Xfinity Support" from the drop-down list which appears. The "Xfinity Support" graphic replaces the "To:" line

• Type your message in the text area near the bottom of the window

• Press Enter to send it

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Please, mark a reply as the Accepted Answer.tick

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3 hours ago

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