Problem with Mail Throttling (RL000003)

Since the end of last week, we have been unable to email comcast.net customers through our mail server, receiving an RL000003 error each time. We've been using the same IP for years and have not had any security incidents that we are aware of. This does not appear to be "rate limiting" as your documentation states, as the mail isn't getting through at all - even at a slow pace - it's just just being rejected until our mail server gives up trying several days later. We even tried buying a new IP for our mail server but it also is receiving the RL000003 error.

Can you please review this and let us know how we can resolve it? Or at minimum, point me to a department that can assist? We tried reaching out to Customer Security Assurance at 1-888-565-4329, but they said that because we weren't Xfinity customers they couldn't help. They laughably suggested that we have our customers that are using comcast.net addresses call Comcast on our behalf to raise the concern.

Thanks in advance for any assistance you can provide.

Errors being received:

From our original IP we've been using for years without issue:
SMTP error from remote mail server after end of data: 421 4.2.0 [Edited: Personal Information] Throttled - try again later. Please see https://postmaster.comcast.net/smtp-error-codes.php#RL000003

From our new IP:
SMTP error from remote mail server after end of data: 421 4.2.0 [Edited: Personal Information] Throttled - try again later. Please see https://postmaster.comcast.net/smtp-error-codes.php#RL000003

Responses

Comcast_MichaelC

Official Employee

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32 Messages

3 months ago

Hey, @user_b15312! Thanks for reaching out to us on the business forums! I apologize to hear that you are having issues with trying to send emails to comcast.net emails. Based on the code it sounds like your server may have been trying to send to many emails at once to the comcast.net domain. As a test to see if your domain is being blocked do you have someone you can send a test email (just one) to see if it goes through?

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user_b15312

New Member

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4 Messages

@Comcast_MichaelC Our server has about 150 emails queued trying to deliver to Comcast at present and it is periodically retrying automatically with still no luck at present. If I try to send to another comcast.net address, it will probably try to send to those other ones again too - but I can try sending another new mail if you'd like?

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3 months ago

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user_b15312

New Member

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4 Messages

For what it's worth, a few days ago I deleted all queued mail that we had and tried to start from scratch with a single message - we still received the same RL000003 error and the message never went through. I thought that would be a sensible thing to try if this was in fact actually "rate limiting", which it does not appear to be.

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3 months ago

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user_b15312

New Member

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4 Messages

I will say that after a week of failures, after posting to the forum and reaching out through the support chat, messages seem to be flowing again. I'm not sure what happened, but I'm happy to see it. I do wish there was a concrete answer as to what happened, but I'll take the win and hope it holds.

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3 months ago

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