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Bounce and Failure Code Quick Reference Guide
Jamie Beliveau 12/10/2021 3:46:00 PM

Bounce vs. Failure

A bounce is when you receive a response as to why your message was not able to be delivered. This is similar to when you receive a letter back that says “return to sender” on the envelope.

A failure to deliver a message at all can happen for a myriad of reasons, which will be detailed further in this document.


There are three types of Bounces: Undeliverable, Block, and Informational.

Undeliverable Bounces

Bounce Reason



Your message encountered an error and was not delivered. Future messages to this recipient may succeed. (i.e. mailbox full, account disabled, exceeds quota, out of disk space, relaying denied)


Your message encountered an error and was not delivered. Future messages to this recipient will fail. (i.e. user unknown, mailbox not found, etc...)


Block Bounces

Bounce Reason



Your message was blocked and further action is necessary to deliver your message. Typically these bounces are sent from spam filters that have quarantined your message, but will deliver it if you follow the instructions in the bounce.


Your message has been identified as spam and was blocked.


Your message contained a virus and was blocked.


Your message was blocked for an unknown or general reason.


Informational Bounces

Bounce Reason



Your message encountered an error, but the error condition may be temporary and delivery attempts are still being made. (i.e. unable to connect to recipient's mail server)


The bounce is an auto-reply. (i.e. out of office, vacation)


The bounce is a subscribe request. (i.e. someone wants to join a mailing list)


The bounce is an unsubscribe request. (i.e. someone wants to be taken off of a mailing list)

Address Change

The bounce is an address change notification.


Your message was modified prior to delivery. (i.e. illegal attachment removed



There are six different failure types in CharityEngine®. Failures can happen for a variety of reasons: a badly formatted email address, the recipient previously marking messages from the sender as spam, or technical issue on the recipient’s end.

Failure Codes

Fail Message


DNS Error

Error communicating to the given email provider or if the recipient’s IT systems (specifically their DNS servers) are not working properly.

Connection Error

Error connecting to a mail server. This happens when mail servers are down or are overloaded and are not accepting any emails.

Response Error

This fail message is displayed when an email server returns an error message. This can happen if a recipient’s mailbox is full or if there are potential IT issues and/or errors on the client's end.

SSL Authentication Error

This failure message occurs when there are IT issues indicating that the client's IP address isn’t being seen as secure on the recipient's end.

Suppression Error

This error is when an email server informs users that an email address is suppressed. Suppressions occur when an email provider communicates that the email is invalid or has reported the sender as spam.

Bad Data Error

This failure is displayed when an email address is invalid. This occurs when incorrect is data associated with the intended email recipient. This could be anything from a fake domain used (i.e. ABC@123.com) or if an email address ported into the system contains items such as two "@" signs.


Blacklists and Suppressions

CharityEngine® will blacklist emails after certain events to ensure that the sender continues to have the best reputation possible with email providers. While it is not recommended, customers can request to have an email address removed from the CharityEngine® blacklist.

It is important to note that there are two blacklists – one that is maintained within the customer’s CharityEngine® that a specific to the send history between the customer and receiving email since being in CharityEngine®. In addition to the customer blacklist, there is a global blacklist that is utilized across all customers. Often the fails listed as Suppression Error are emails that are listed in CharityEngine®’s global blacklist.


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