4XX Error codes

Error message Description Resolution
You can only send xx msgs per xx The sender has been ratelimited. Reduce the sending speed, try again after the specified period

5XX Error codes

Error message Description Resolution
The sender xxx.xxx.xxx.xxx is banned The sender's IP address has been added to the banned senders list The address will need to be removed from the banned senders list
 
The domain example.com is banned The sender's domain name has been added to the banned senders list The address will need to be removed from the banned senders list
 
Dictionary attack detected The system has detected an attempt to harvest email addresses Send email to only existing addresses only our update your mailing list
 
Legitimate bounces are never sent to more than one recipient. The sender's sent a bounce message to more than one address
 
Restricted characters in address The email address contains characters that should not be used Check the email address
 
Sender verification failed The senders email address could not be verified Ensure that the email address you use for sending does accept email
 
Recipient verification failed The recipient email address could not be verified Check the email address you are sending to
 
Relay not permitted The sender is not authorised to send email via the server. Request the administrator to add the sender to relay settings
 
The email address does not exist The checks have determined that the email address does not exist The sender must resend the email to a valid recipient address.
 
The sender is in a black list rbl.baruwa.net The sender is listed in the rbl.baruwa.net DNS blacklist This list does not accept removal requests, the address will be removed automatically when the amount of unsolicited email reduces.
 
The sender is in a black list rbl.baruwa.net The sender is listed in the rbl.baruwa.net DNS blacklist This list does not accept removal requests, the address will be removed automatically when the amount of unsolicited email reduces.
 
The sender is in a black list hostkarma.junkemailfilter.com The sender is listed in the hostkarma.junkemailfilter.com DNS blacklist The sender should request removal of the associated address via the website - http://ipadmin.junkemailfilter.com/remove.php
 
The sender is in a black list bl.spameatingmonkey.net The sender is listed in the bl.spameatingmonkey.net DNS blacklist The sender should request removal of the associated address via the website - http://spameatingmonkey.com/delist.html
 
The sender is in a black list zen.spamhaus.org The sender is listed in the zen.spamhaus.org DNS blacklist The sender should request removal of the associated address via the website - http://www.spamhaus.org/lookup/
 
The sender is in a black list bl.spamcop.net The sender is listed in the bl.spamcop.net DNS blacklist The sender should request removal of the associated address via the website - https://www.spamcop.net/bl.shtml
 
The sender is in a black list cbl.abuseat.org The sender is listed in the cbl.abuseat.org DNS blacklist The sender should request removal of the associated address via the website - http://cbl.abuseat.org/lookup.cgi
 
The message failed SPF checks The sender's is not authorised to send messages for the domain Check the domain SPF record or send from authorised hosts only.
 
The sender xxx.xxx.xxx.xxx has no reverse DNS record The sender's IP address does not have a PTR record Create a reverse DNS record for the sending IP address
 
Blacklisted file extension detected. The message contains an executable which should not be sent via email. Do not send executables via email
 
The message was rejected due to security policies The message triggered an Anti-Virus Engine signature Check your computer or the message
 
This message is administratively prohibited The message was rejected because it contains a subject that is prohibited or contains a blank reply-to header. Add the sender to Empty Reply Checks Exemptions List
 
The sender did not present a HELO/EHLO greeting The sender did not present a HELO/EHLO greeting Configure your client to send a HELO/EHLO message
 
The sender presented HELO as an IP address The sender used an IP address as the HELO/EHLO message (See RFC2821 4.1.3) Configure your client not to send an IP address as the HELO/EHLO message
 
DKIM failure: xx The email failed DKIM checks Ensure that your DKIM policy is correct and that you are signing all messages
 
Authentication is allowed only once per message Authentication is allowed only once per message in order to slow down brute force cracking Ensure that your SMTP authentication credentials are correct
 
The sender is blacklisted due to repeated auth failures The sender is locally blacklisted for a brute force auth (username+password) cracking attempt Ensure that your SMTP authentication credentials are correct
 
TLS is required The sender connected without TLS encryption Ensure that your client connects using TLS encryption
 
This message contains invalid headers This message contains invalid headers, Message header names should be ASCII. Ensure your client sends correctly formated headers using ASCII