Email Bounce Codes

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Traditional Bounce Codes

When you add the Email Invalid Cause to display as a Column to any of your Deliverability Smartlists, you will see a code value, and potentially a suffix as well, to help you understand the reason for the Bounce.

• Codes in the 400 range are generally Soft Bounces
• Codes in the 500 range are generally Hard Bounces

Mail server administrators can create custom messages that accompany bounce codes

Code	Explanation
250	Mail accepted by receiving network
421	<domain> Service not available, closing transmission channel
450	Requested mail action not taken: mailbox unavailable (e.g., mailbox busy)
451	Requested action aborted: error in processing
452	Requested action not taken: insufficient system storage
500	The server could not recognize the command due to a syntax error.
501	A syntax error was encountered in command arguments.
502	This command is not implemented.
503	The server has encountered a bad sequence of commands.
504	A command parameter is not implemented.
550	User’s mailbox was unavailable (such as not found)
551	The recipient is not local to the server.
552	The action was aborted due to exceeded storage allocation.
553	The command was aborted because the mailbox name is invalid.
554	The transaction failed for some unstated reason.

 

 

Enhanced Bounce Codes

If a suffix appears after one of the codes above, it is an enhanced Bounce code

Mail server administrators can crate custom messages that accompany bounce codes

Code	Explanation
5.0.0	Address does not exist
5.1.0	Other address status
5.1.1	Bad destination mailbox address
5.1.2	Bad destination system address
5.1.3	Bad destination mailbox address syntax
5.1.4	Destination mailbox address ambiguous
5.1.5	Destination mailbox address valid
5.1.6	Mailbox has moved
5.1.7	Bad sender’s mailbox address syntax
5.1.8	Bad sender’s system address
5.2.0	Other or undefined mailbox status
5.2.1	Mailbox disabled, not accepting messages
5.2.2	Mailbox full
5.2.3	Message length exceeds administrative limit.
5.2.4	Mailing list expansion problem
5.3.0	Other or undefined mail system status
5.3.1	Mail system full
5.3.2	System not accepting network messages
5.3.3	System not capable of selected features
5.3.4	Message too big for system
5.4.0	Other or undefined network or routing status
5.4.1	No answer from host
5.4.2	Bad connection
5.4.3	Routing server failure
5.4.4	Unable to route
5.4.5	Network congestion
5.4.6	Routing loop detected
5.4.7	Delivery time expired
5.5.0	Other or undefined protocol status
5.5.1	Invalid command
5.5.2	Syntax error
5.5.3	Too many recipients
5.5.4	Invalid command arguments
5.5.5	Wrong protocol version
5.6.0	Other or undefined media error
5.6.1	Media not supported
5.6.2	Conversion required and prohibited
5.6.3	Conversion required but not supported
5.6.4	Conversion with loss performed
5.6.5	Conversion failed
5.7.0	Other or undefined security status
5.7.1	Delivery not authorized, message refused
5.7.2	Mailing list expansion prohibited
5.7.3	Security conversion required but not possible
5.7.4	Security features not supported
5.7.5	Cryptographic failure
5.7.6	Cryptographic algorithm not supported
5.7.7	Message integrity failure

Not all mail servers adhere to these standards.