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Email Error Codes

Details

Refer to the table below to learn about email error codes and how to resolve issues.
 

Error Code Description Resolution
CXBL The sending IP address has been blocked by Cox due to exhibiting spam-like behavior. Send an email request to Cox to ask for a sending IP address be unblocked.

Note: Cox has sole discretion whether to unblock the sending IP address.
CXDNS There was an issue with the connecting IP address Domain Name System (DNS).

The Reverse DNS (rDNS) lookup for your IP address is failing.

  • Confirm the IP address that sends your email.
  • Check the rDNS of that IP address. If it passes, then wait 24 hours and try resending your email.
CXSNDR There was a problem with the sender's domain. Your email failed authentication checks against your sending domain's SPF, DomainKeys, or DKIM policy.
CXSMTP There was a violation of SMTP protocol. Your email wasn't delivered because Cox was unable to verify that it came from a legitimate email sender.
CXCNCT There was a connection issue from the IP address. There is a limit to the number of concurrent SMTP connections per IP address to protect the systems against attack. Ensure that the sending email server is not opening more than 10 concurrent connections to avoid reaching this limit.
CXMXRT The sender has sent email to too many recipients and needs to wait before sending more email. The email sender has exceeded the maximum number of sent email allowed.
CDRBL The sending IP address has been temporarily blocked by Cox due to exhibiting spam-like behavior. The block duration varies depending on reputation and other factors, but will not exceed 24 hours. Inspect email traffic for potential spam, and retry email delivery.
IPBL0001 The sending IP address is listed in the Spamhaus Zen DNSBL. Refer to Spamhaus for more information and removal instructions. Spamhaus has sole discretion whether to remove the sending IP address from the DNSBL.
IPBL0010 The sending IP is listed in the Return Path DNSBL. Refer to Return Path for more information and removal instructions. Return Path has sole discretion whether to remove the sending IP address from the DNSBL.
IPBL0100 The sending IP is listed in the Invaluement ivmSIP DNSBL. Refer to ivmSIP for more information and removal instructions. ivmSIP has sole discretion whether to remove the sending IP address from the DNSBL.
IPBL0011 The sending IP is in the Spamhaus Zen and Return Path DNSBLs. Refer to the instructions above for error codes IPBL0001 and IPBL0010.
IPBL0101 The sending IP is in the Spamhaus Zen and Invaluement ivmSIP DNSBLs. Refer to the instructions above for error codes IPBL0001 and IPBL0100.
IPBL0110 The sending IP is in the Return Path and Invaluement ivmSIP DNSBLs. Refer to the instructions above for error codes IPBL0010 and IPBL0100.
IPBL0111 The sending IP is in the Spamhaus Zen, Return Path and Invaluement ivmSIP DNSBLs. Refer to the instructions above for error codes IPBL0001, IPBL0010, and IPBL0100.
IPBL1000 Cloudmark CSI Suspect / CSI Global The sending IP address is listed on a CSI blacklist. You can check your status on the CSI website.
IPBL1001 The sending IP is listed in the Cloudmark CSI and Spamhaus Zen DNSBLs. Refer to the instructions above for error codes IPBL1000 and IPBL0001.
IPBL1010 The sending IP is listed in the Cloudmark CSI and Return Path DNSBLs. Refer to the instructions above for error codes IPBL1000 and IPBL0010.
IPBL1011 The sending IP is in the Cloudmark CSI, Spamhaus Zen and Return Path DNSBLs. Refer to the instructions above for error codes IPBL1000, IPBL0001, and IPBL0010.
IPBL1100 The sending IP is listed in the Cloudmark CSI and Invaluement ivmSIP DNSBLs. Refer to the instructions above for error codes IPBL1000 and IPBL0100.
IPBL1101 The sending IP is in the Cloudmark CSI, Spamhaus Zen and Invaluement IVMsip DNSBLs. Refer to the instructions above for error codes IPBL1000, IPBL0001, and IPBL0100.
IPBL1110 The sending IP is in the Cloudmark CSI, Return Path and Invaluement ivmSIP DNSBLs. Refer to the instructions above for error codes IPBL1000, IPL0010, and IPBL0100.
IPBL1111 The sending IP is in the Cloudmark CSI, Spamhaus Zen, Return Path and Invaluement ivmSIP DNSBLs. Refer to the instructions above for error codes IPBL1000, IPBL0001, IPBL0010, and IPBL0100.
IPBL00001 Spamhaus ZEN The sending IP address is listed on a Spamhaus blacklist. Check your status at Spamhaus.
URLBL011 A URL within the body of the message was found on blocklists SURBL and Spamhaus DBL.
  • Refer to SURBL for more information and removal instructions.
  • Refer to Spamhaus for DBL information and removal instructions
URLBL101 A URL within the body of the message was found on blocklists SURBL and ivmURI.
  • Refer to SURBL for more information and removal instructions.
  • Refer to ivmURI for more information and removal instructions
URLBL110 A URL within the body of the message was found on blocklists Spamhaus DBL and ivmURI.
  • Refer to ivmURI for more information and removal instructions.
  • Refer to Spamhaus for DBL information and removal instructions
URLBL1001 Spamhaus DBL The URL is listed on a Spamhaus blacklist. Check your status at Spamhaus.
421 - [ESMTP server temporarily not available] Our systems are experiencing an issue which is causing a temporary inability to accept new email. Retry your mailings at a later time.
421 - [too many sessions from <source IP>] The sending IP address has exceeded the five maximum concurrent connection limit. Configure your sending server to establish no more than five concurrent connections.
554 - [ESMTP no data before greeting] The sending server has attempted to communicate too soon within the SMTP transaction. Ensure that your sending server is RFC 5321-compliant, and is following the proper SMTP protocol standards.
554 - [<source IP> rejected - no rDNS] Cox requires that all connecting email servers contain valid reverse DNS PTR records. Ensure that your sending email servers have a valid reverse DNS entry.
554 - [cox too many bad commands from <source IP>] An email client has repeatedly sent bad commands or invalid passwords resulting in a three-hour block of the client's IP address. Check the password used by your email client and consider using an alternate email client if your password is correct.
421 - [<source IP> DNS check failure - try again later] The reverse DNS check of the sending server IP address has failed. Ensure that your DNS configuration is correct and that the PTR record is resolvable.
452 - [<mailfrom address> requested action aborted: try again later] The SMTP connection has exceeded the 100 email message threshold and was disconnected. Establish a new connection and continue sending.
550 - [<mailfrom address> sender rejected] Cox requires that all sender domains resolve to a valid MX or A-record within DNS. Ensure that your domain has a valid MX or A-record within DNS.
550 - [<recipient email> recipient rejected] The intended recipient is not a valid Cox Email account. Ensure that your mailing list is up-to-date with verified recipient email addresses.
552 - [$(_id) attachment extension is forbidden] The message has been rejected because it contains an attachment with one of the following prohibited file types, which commonly contain viruses: .shb, .shs, .vbe, .vbs, .wsc, .wsf, .wsh, .pif, .msc, .msi, .msp, .reg, .sct, .bat, .chm, .isp, .cpl, .js, .jse, .scr, .exe. Ensure that your mailings do not contain attachments with these file types.
452 - [<source IP> rejected. Too many invalid recipients] The sending IP address has exceeded the threshold of invalid recipients and has been blocked. Ensure that your mailing list is up-to-date with verified recipient email addresses, and try again at a later time.
452 - [Message threshold exceeded] Cox enforces various rate limits to protect our platform. The sending IP address has exceeded one of these rate limits and has been temporarily blocked. Slow down the rate at which you attempt to send email.

Contacting Cox for Assistance

If you are having problems with email delivery to Cox, and you were unable to resolve your problem using the steps in the Error Codes section above, send us an email at unblock.request@cox.net for assistance. Your email must contain all of the following information in order for us to process your request.

  • First name
  • Last name
  • Email address
  • Phone number
  • Domain
  • IP/CIDR range of outgoing email servers
  • From the following choices, indicate the item that best describes the issue you are experiencing.
    • My IP address is being blocked
    • My domain is being blocked
    • My email is being marked as spam
    • My email is not arriving to the intended recipients
    • My email is being delayed
    • Other
  • Include a detailed description of the issue you are experiencing, such as the date and time when the problem began and the corrective action that has been taken.
  • Include email server logs related to the issues.

 

Note: Due to the technical nature of the requested information, this email should be submitted by an email administrator or other technical contact that is familiar, and can obtain, all of the requested details.

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