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Classified Bounces List

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    Overview

    Mailgun Optimize's Bounce Classification feature helps to identify critical bounces that lower your email reputation and cause other problems with your sending. The feature not only classifies these bounces by sending domain and mailbox provider/spam filter but also provides the relevant error message as well as recommended solution.

    As such, we term a bounce processed by this feature as a Classified Bounce. Because the email landscape is always changing, the bounces we classify are also dynamic. This article will provide you with the most up-to-date information regarding the current list of classified bounces.

     

    List of Classified Bounces

    Below is a list of all Classified Bounces currently processed by our Bounce Classification feature. 

    Mailbox Provider / Spam Filter
    Category

    Code

    Sample Error Message
    Apple ESPBLOCK 554 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137
    Apple BLACKLISTED 550 smtp;550 5.7.1 Your email was rejected due to having a domain present in the Spamhaus DBL -- see https://www.spamhaus.org/dbl/
    ATT BLACKLISTED 553 5.3.0 flpd568 DNSBL:RBL 521< x.xx.xx.xx >_is_blocked.For assistance forward this error to abuse_rbl@abuse-att.net
    Barracuda BLACKLISTED 554 smtp; 554 rejecting banned content
    Cloudmark BLACKLISTED 554 smtp; 554 mcc-ibgw-6001a.ext.cloudfilter.net cmsmtp [x.xx.xx.xx] is listed on Cloudmark CSI-Global. Please visit https://csi.cloudmark.com/en/reset AUP#RBL
    Cloudmark BLACKLISTED 550 smtp; 550 5.7.1 Service unavailable; client [x.xx.xx.xx] blocked using Cloudmark Sender Intelligence (Visit https://csi.cloudmark.com/reset-request/ if you feel this is in error.). Please provide the following IP address when reporting problems: [x.xx.xx.xx]
    Cloudmark BLACKLISTED 550 smtp; 550 5.7.1 Service unavailable; client [x.xx.xx.xx] blocked using Proofpoint Dynamic Reputation (Visit https://ipcheck.proofpoint.com/ if you feel this is in error.).
    Comcast BLACKLISTED 554 [x.xx.xx.xx] found on one or more DNSBLs, see https://postmaster.comcast.net/smtp-error-codes.php#BL000100
    Comcast ESPBLOCK 554 5.1.0 xx.xx.xx.x Comcast block for spam. Please see https://postmaster.comcast.net/smtp-error-codes.php#BL000000
    EOP (Exchange Online Protection) BLACKLISTED 550 smtp; 550 5.7.1 Service unavailable, Client host [x.xx.xx.xx] blocked using Spamhaus. To request removal from this list see https://www.spamhaus.org/query/ip/x.xx.xx.xx (AS3130).
    EOP (Exchange Online Protection) BLACKLISTED 550 smtp; 550 5.7.606 Access denied, banned sending IP [x.xx.xx.xx]. To request removal from this list please visit https://sender.office.com/ and follow the directions. For more information please go tohttp://go.microsoft.com/fwlink/?LinkID=526655 AS(1430)
    Free ESPBLOCK 550 Too many spams from your IP (x.xx.xx.xx), please visit http://postmaster.free.fr/
    Gmail ESPBLOCK 550 smtp;550 5.7.1 [x.xx.xx.xx] Our system has detected that this message is likely suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked. Please visit https://support.google.com/mail/answer/ for more information. - gsmtp
    Gmail ESPBLOCK 550 smtp;550 5.7.1 [x.xx.xx.xx] Our system has detected that this message is likely suspicious due to the very low reputation of the sending IP. To best protect our users from spam, the message has been blocked.
    Gmail ESPBLOCK 550 smtp;550 5.7.1 [x.xx.xx.xx] Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail, this message has been blocked. Please visit https://support.google.com/mail/?p=UnsolicitedMessageError for more information. - gsmtp
    Gmail ESPBLOCK 421 421 4.7.28 Gmail has detected an unusual rate of unsolicited mail originating from your DKIM domain. To protect our users from spam, mail sent from your domain has been temporarily rate limited. Please visit https://support.google.com/mail/?p=UnsolicitedRateLimitError to review our Bulk Email Senders Guidelines.
    Gmail ESPBLOCK 552 5.7.0 This message was blocked because its content presents a potential security issue. Please visit https://support.google.com/mail/?p=BlockedMessage to review our message content and attachment content guidelines.
    Gmail ESPBLOCK 550 5.7.26  https://support.google.com/mail/?p=DmarcRejection - gsmtp
    Gmail GENERIC 421 4.7.26 This mail has been rate limited because it is unauthenticated. Gmail requires all senders to authenticate with either SPF or DKIM.
    Authentication results:
    DKIM = did not pass
    SPF [example.com] with ip: [xx.xx.xx.x] = did not pass
    For instructions on setting up authentication, go to https://support.google.com/mail/answer/81126#authentication - gsmtp
    Gmail GENERIC 421 4.7.27 This mail has been rate limited because SPF does not pass. Gmail requires all large senders to authenticate with SPF. 
    Authentication results: 
    SPF [domain.com] with ip: [xx.xx.xx.x] = did not pass
    For instructions on setting up SPF authentication, go to https://support.google.com/a/answer/10685031 - gsmtp
    Hotmail BLACKLISTED 550 5.7.1 Service unavailable, MailFrom domain is listed in Spamhaus. To request removal from this list see https://www.spamhaus.org/query/lookup/
    Hotmail ESPBLOCK 550 5.7.1 Unfortunately, messages from [x.xx.xx.xx] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.
    Invaluement BLACKLISTED 550 Connection refused. RBL [IP-x.xx.xx.xx] Blocked by Invaluement - see https://www.invaluement.com/research/
    Outlook ESPBLOCK 451 451 4.7.650 The mail server [x.xx.xx.xx] has been temporarily rate limited due to IP reputation. For e-mail delivery information, see https://postmaster.live.com (S843)[#.prod.protection.outlook.com]
    Outlook ESPBLOCK 550 smtp;550 5.7.1 Unfortunately, messages from [x.xx.xx.xx] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [#.eop-nam02.prod.protection.outlook.com]
    Spamcop BLACKLISTED 550 Service unavailable; Client host [example.com] blocked by bl.spamcop.net; xx.xx.xx.x (example.com:blocked)
    Yahoo ESPBLOCK 554 smtp;554 Message not allowed - [PH01] Email not accepted for policy reasons. Please visit https://postmaster.yahooinc.com/error-codes
    Yahoo ESPBLOCK 553 smtp; 553 5.7.1 [TSS07] Connections will not be accepted from [x.xx.xx.xx], because the ip is in Spamhaus's list; see https://postmaster.yahooinc.com/error-codes
    Yahoo ESPBLOCK 554 5.7.9 Message not accepted for policy reasons. See https://postmaster.yahooinc.com/error-codes

     

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