Pardot Knowledge Base

Bounce Codes Reference

Last Updated: May 26, 2016 | Print this Article
There are an unlimited number of bounce replies. This article doesn't provide a definitive list of all bounce replies -- just an overview of the most common ones. Since the bounce codes are not generated by Pardot, the explanation from our Support team will be limited to the table below. You'll need to contact the recipient’s mail server administrator for clarification regarding bounce messages from that server. You can also find resources online for more information about individual bounce codes.

What are bounce messages?

A bounce message (or code) is a reply from the receiving mail server describing why the email was not delivered. Sometimes, messages accompanying codes are non-standard (mail server administrators can customize these messages); therefore, messages may be different from each receiving mail server you attempted to contact.

What does Pardot do with bounce messages?

Once we receive a bounce message from a mail server, we use the bounce code to determine if the bounce is a hard bounce (permanent failure) or a soft bounce (temporary failure). We will automatically opt-out prospects who have had a hard bounce.

Are there different types of bounce codes?

The traditional SMTP bounce reasons are three-digit codes (e.g., 550). The enhanced SMTP bounce responses are three-digits separated by decimal points (e.g., 5.1.1). You may see both in the bounce reasons for a given email campaign.

How do I access my bounce report?

You can access the bounce report by visiting Reports > Emails and drilling down into the hyperlinked number of soft or hard bounces in the individual list email report, drip program report, or email template report you would like to review.

Traditional Bounce Codes

Code Explanation
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.
*Mail server administrators can customize messages that accompany bounce codes. Resource: RFC2821 (April 2001); What those SMTP Error Codes Mean and Why You Should Care (Getting Email Delivered, January 2010)

Enhanced Bounce Codes

Code Explanation
5.0.0 Unknown issue
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
*Mail server administrators can customize messages that accompany bounce codes. Resource: RFC3463 (January 2003); SMTP Enhanced Codes Registry (IANA, February 2012)

Bounce Codes for Popular Services

Not what you're looking for? Check out these other articles:
Bounce Management Overview
Viewing Bounce Reports
How to Keep Your Email Lists Sparkling Clean

Need more? Start a conversation with other Pardot users in our Success Community