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Email Campaign: Investigating Failed Email Delivery
Authored by:
on 9/11/2023 1:17:00 PM


While failed emails may be unavoidable when sending an email initiative, it is important to investigate why the email failed. Understanding email failures will assist in greater deliverability rates, improve sending rates, and most importantly the ability to ensure you are reaching your donors. 


While this article is informational, having access to an existing email initiative will be helpful to compare sending results. 

Instructions: How to identify failed emails via Initiatives Listing Screen

Step 1: Navigate to the Campaigns App > Create & Publish > Initiatives > locate the email initiative you wish to review. 

Step 2: Navigate to click on the number next to Fail and you will be redirected to a Send Failures summary. 

You will be navigated to the fail analytics page and will be able to view why the email failed to send. In the below example, there was a DNS Error, 4 previous fails, and the contact was not blacklisted.

Instructions: How to read the Send Failures Report

Step 1: Review the REASON code to determine why the email failed to send to the Email Service Provider (ESP). Reason detail can be found here within the Bounce and Failure Code Quick Reference Guide

Resource: Email Failures - Defined
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.


Resource: Blacklists and Suppressions - Defined

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.

Resource: Bounces - Defined

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.

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 was blocked as user reported spam or unsubscribe through Email Service Provider.

ESP Bad Data

Your message was blocked due to invalid data response from ESP (email service provider).


Your message was blocked due to attempts exceeded maximum failures of any type and have had no successful sends.


Your message was blocked due to attempts exceeded maximum failures and have had no successful sends.


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


FAQs & Further Reading

Q. Is there another avenue to easily review email initiative results?
A. Yes. By accessing the Reports & Analytics App > Campaigns > Send Failures to see each summary of all failures. Alternatively, you can navigate to Reports & Analytics App > Campaign > Initiative Analytics to view all email initiatives send summaries. 
Q. What actions should I take with blacklisted emails?
A. Managing your email list is crucial for not only reaching your constituents but for also managing your reputation as a sender. CharityEngine has integrated several technology tools to assist you in list management. Our outbound email delivery technology actively tracks and reports on responses in which the email address is reported as invalid. Once confirmed as invalid, CharityEngine will identify the user’s email address to prevent future email delivery failures. Read more here regarding email blacklisting. 

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