emails to comcast users getting bounced...

One of my clients sends mailing lists out (maybe 1-2x a week) and there are less than 10 comcast users on the list.
They are starting to see regular bouncebacks with:
550 5.4.300 Message expired -> 451 4.2.0 Throttled - https://postmaster.comcast.net/smtp-error-codes.php#RL000010‎

and

550 5.4.318 Message expired, connection reset (SuspiciousRemoteServerError), 450 4.4.318 Connection was closed abruptly (SuspiciousRemoteServerError)‎

the domain sending the messages is hosted by MS so should be reputable...

with less than 10 comcast users (but not less than 10 total) i wouldn't think it would be a "mailing list" issue...but i thought i'd reach out for any ideas.

thanks

Responses

XfinityAldrik

Official Employee

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2.1K Messages

5 months ago

Thank you for reaching out to us @user_f20c31! For Comcast Email Error Codes and Messages, we have a dedicated article here.

Mail servers are typically shared by many users, so it may be the case that another party using your mail server has sent spam, even if you haven’t. Removal requests can be sent to http://postmaster.comcast.net/smtp-error-codes.php and will require the IP address of the blocked mail server.

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user_f20c31

Visitor

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4 Messages

@XfinityAldrik thank you. IT admin here as well...i know all about the shared server issue..i was looking for the submission form.

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5 months ago

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XfinityJosephA

Official Employee

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1.7K Messages

user_f20c31 you're welcome 😀 Our support with this type of issue is a little more limited. Our Customer Security Assurance team is more equipped to review this a little further. They can be reached at 1-888-565-4329, 8:00am - 12:00am EST, 7 days a week.

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5 months ago

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user_f20c31

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@XfinityJosephA shouldn't i at least get some type of reply from the form i submitted?
additionally will they even talk to me since i am the sender and not the comcast user?

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5 months ago

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XfinityMarcus

Official Employee

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1.4K Messages

user_f20c31 great questions, and to know for sure what I would recommend is just reaching back out to them for a direct follow-up using that number we shared. You can also find their contact information using this hyperlink.

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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.
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5 months ago

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user_f20c31

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4 Messages

5 months ago

i also hope ipv6 addresses can be used...as that's all i could extract from the message headers.

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user_f20c31

emails to comcast users getting bounced...

XfinityAldrik

user_f20c31

XfinityJosephA

user_f20c31

XfinityMarcus

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