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Error code wiki · 33 codes

Comcast SMTP error codes

Comcast runs Xfinity's consumer email, so mail to comcast.net addresses is received and filtered by Xfinity's mail servers.

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Permanent failures (5xx)

6 codes

The receiving server refused the message for good. Your server will not try again, and the message comes back to you as a bounce.

  1. 550Not an Xfinity customer.The address you sent to does not belong to an Xfinity customer. The failure is permanent, and Xfinity asks bulk mailers to treat it as an unsubscribe.Permanent
  2. 550Too many invalid recipients.Xfinity refused the whole message because too many of its recipients were invalid, so nobody received it. Clean the recipient list and send it again.Permanent
  3. 550Sender domain has no A or MX record.Xfinity refused the message because the domain you send from has neither an A record nor an MX record in DNS. Add one and send again.Permanent
  4. 550Account not available.The Xfinity account you wrote to is currently not available. Xfinity sends this as a 550, so the message has failed, though the account itself may come back.Permanent
  5. 552Message too large.The message is larger than Xfinity accepts. Xfinity takes messages of 15 MB or smaller, so reduce the size and send it again.Permanent
  6. 554No reverse DNS (PTR) record.Xfinity refused the connection because your sending IP has no PTR record. Every server sending to Xfinity needs valid reverse DNS, so the owner of the IP must add one.Permanent

Temporary failures (4xx)

4 codes

The receiving server cannot take the message now. Your server keeps it and retries, and only bounces it if the retries run out.

  1. 421Try again later.Xfinity turned the message away for now with a generic 421. Treat it as temporary and let your server retry: Xfinity uses it for several reasons it does not spell out.Temporary
  2. 421Reverse DNS lookup failed.Xfinity could not complete a reverse DNS lookup for your sending IP. It treats this as temporary, so your server should retry, but a broken DNS setup keeps it failing.Temporary
  3. 452Too many emails in one session.Your server sent more messages in one SMTP session than Xfinity accepts. Xfinity allows 1,000 emails per session, so the rest have to go in a new session.Temporary
  4. 452Too many recipients in one message.The message listed more recipients than Xfinity accepts at once. Xfinity allows 100 recipients per message, so a larger list has to be split.Temporary

Provider references

23 codes

Tags the provider prints in its replies without a standard code of their own.

  1. BL000000Blocked for spam-like sending patterns.Xfinity's filters saw mail from your server sent in patterns that look like spam, and blocked the server from sending to Xfinity addresses. Removal requests go through Xfinity's Postmaster site.
  2. BL000001Listed on Spamhaus ZEN.Xfinity refused the message because your sending IP is listed on Spamhaus ZEN. Request removal from that list after fixing what caused the listing.
  3. BL000010Listed on CSI.Xfinity refused the message because your sending IP is listed on CSI. Request removal from that list after fixing what caused the listing.
  4. BL000011Listed on CSI and Spamhaus ZEN.Xfinity refused the message because your sending IP is listed on CSI and Spamhaus ZEN. Request removal from each of those lists after fixing what caused the listing.
  5. BL000100Listed on Return Path.Xfinity refused the message because your sending IP is listed on Return Path. Request removal from that list after fixing what caused the listing.
  6. BL000101Listed on Return Path and Spamhaus ZEN.Xfinity refused the message because your sending IP is listed on Return Path and Spamhaus ZEN. Request removal from each of those lists after fixing what caused the listing.
  7. BL000110Listed on Return Path and CSI.Xfinity refused the message because your sending IP is listed on Return Path and CSI. Request removal from each of those lists after fixing what caused the listing.
  8. BL000111Listed on Return Path, CSI and Spamhaus ZEN.Xfinity refused the message because your sending IP is listed on Return Path, CSI and Spamhaus ZEN. Request removal from each of those lists after fixing what caused the listing.
  9. BL001000Listed on VTL.Xfinity refused the message because your sending IP is listed on VTL. Request removal from that list after fixing what caused the listing.
  10. BL001001Listed on VTL and Spamhaus ZEN.Xfinity refused the message because your sending IP is listed on VTL and Spamhaus ZEN. Request removal from each of those lists after fixing what caused the listing.
  11. BL001010Listed on VTL and CSI.Xfinity refused the message because your sending IP is listed on VTL and CSI. Request removal from each of those lists after fixing what caused the listing.
  12. BL001011Listed on VTL, CSI and Spamhaus ZEN.Xfinity refused the message because your sending IP is listed on VTL, CSI and Spamhaus ZEN. Request removal from each of those lists after fixing what caused the listing.
  13. BL001100Listed on VTL and Return Path.Xfinity refused the message because your sending IP is listed on VTL and Return Path. Request removal from each of those lists after fixing what caused the listing.
  14. BL001101Listed on VTL, Return Path and Spamhaus ZEN.Xfinity refused the message because your sending IP is listed on VTL, Return Path and Spamhaus ZEN. Request removal from each of those lists after fixing what caused the listing.
  15. BL001110Listed on VTL, Return Path and CSI.Xfinity refused the message because your sending IP is listed on VTL, Return Path and CSI. Request removal from each of those lists after fixing what caused the listing.
  16. BL001111Listed on VTL, Return Path, CSI and Spamhaus ZEN.Xfinity refused the message because your sending IP is listed on VTL, Return Path, CSI and Spamhaus ZEN. Request removal from each of those lists after fixing what caused the listing.
  17. DM000001Rejected by the sender's DMARC policy.Xfinity rejected the message because it passed neither SPF nor DKIM for the sending domain, and it applied that domain's published DMARC policy.
  18. ES000001Sending from an Xfinity residential IP.Xfinity blocked mail sent from a dynamic or residential Xfinity IP address by a server other than smtp.comcast.net. Send through Xfinity, or use a business connection.
  19. ES000010Dynamic or residential IP address.Xfinity blocked the connection because your server sends from IP space it considers dynamic or residential, in most cases because the reverse DNS name does not look static.
  20. ODM00001Rejected by Xfinity's own DMARC policy.Xfinity's outgoing mail servers refused the message under Xfinity's own published DMARC policy, because it passed neither DKIM nor SPF for the domain.
  21. RL000001Rate limited by sender reputation.Xfinity is slowing mail from your server with a temporary 4xx because it passed the hourly recipient limit Xfinity sets from your SenderScore. Your server should retry later.
  22. RL000002Rate limited by Cloudmark reputation.Xfinity is slowing mail from your server with a temporary 4xx, using a limit set from Cloudmark's reputation and volume data. A new IP starts low and its limit grows daily.
  23. RL000003Rate limited by sending history.Xfinity is slowing mail from your IP with a temporary 4xx, using a limit set from the IP's past volumes and their quality. It applies to IPv4 and IPv6 alike.

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