Visitor
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1 Message
Domain being throttled
I'm the Email Admin for a reputable domain that is being throttled. We are receiving this error message "[Edited: "Personal Information"] delayed. Reason: 4.3.2 - Not accepting messages at this time ('421', ['4.1.0 162.129.199.120 Throttled - try again later. Please see https://postmaster.comcast.net/smtp-error-codes.php#RL000003'" We have several gateways and all messages are being DKIM signed, we have DMARC and SPF records published as well. The IP addresses for there gateways have been around over 20+ years. An are now experineing this issue. We are a Hospital and University an need some assistance to reduce the throttling. Already check the postmaster.comcast.net site it didnt help.
XfinityRichard
Official Employee
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2.8K Messages
14 days ago
Hi there, @user_xqbb0m I apologize for the trouble you are running into. Since it's been a few days since you last posted, are you still having the same issues?-Richard
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Again
Expert
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33.4K Messages
13 days ago
@user_xqbb0m
This may give you some information.
https://www.xfinity.com/support/articles/email-errors
RL000003
Comcast has instituted rate limiting on all inbound email traffic. This step was taken to protect our customers and our email system from unwanted spam and malicious attacks. Any systems affected by this rate limit will receive a 4xx message (temp-fail) during the SMTP transaction. This message is designed to instruct the sending server to try again at a later time to deliver its email.
This rate limiting policy is based on historical volumes and quality of that volume. The limits applied are independent of the number of domains originating from a given IP. This policy should apply to both IPv4 and IPv6.
New IP addresses that are expected to send significant amounts of email to Comcast subscribers should start by sending low volumes of mail, increasing as time goes on. As your IP sends more email, its limit will increase daily.
If the rate-limit is impacting your ability to deliver email, shortening your server's delivery retry interval should resolve the issue.
If you require additional assistance, please contact Customer Security Assurance at 1-888-565-4329.
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