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"Not Delivering to Previously Bounced Address"

It's 5 o'clock somewhere, and your business associate Sir Not-Appearing-In-This-Film calls you in a panicked state saying they never received an email you promised earlier that day.  Being the savvy Mailgun user you are, you look inside your Mailgun Logs (or alternate monitoring method), and you notice his email failed with the message "Not delivering to previously bounced address." 

So, what does this error mean, and how can Sir Not-Appearing-In-This-Film begin to receive your emails once again?  Don't worry; we'll explain everything you need to know below!

TL;DR Overview

Removing the email address from the Suppressions list of the Mailgun Control Panel will allow delivery of new messages to said address, as long as the address no longer has any issues.

The Cause

This error indicates that the email address is currently suppressed by our system from further delivery attempts. Why?  Because during a previous delivery attempt to this mailbox, the recipient's email provider returned an error to us indicating that the mailbox/email-address does not exist, or is invalid for some reason.  As such, we suppress the address to protect both your and our sending reputation.  High bounce rates negatively impact sending reputation, which in turn lessens your chances of optimal deliverability significantly.

The Solution

If the recipient's email address actually exists and any underlying issues with their mailbox have been fully addressed, you can remove the address from the Suppressions list (or via the Bounces API using an HTTP DELETE request). 

Inside the Mailgun Control Panel (options displayed down the left-hand side on a dark column), use the following instructions:

  1. Click on the Sending option on the left-hand side of your Mailgun dashboard.
  2. Click on the specific domain for which you would like to view the Suppressions.
  3. You will click on the Suppressions option.
  4. Choose the Bounces suppression type and then click Delete button on the right-hand side of the specific suppression you would like to delete.

Simply mark the checkbox next to the recipient and use the delete button to remove the suppression.  Once removed, new messages that you send to the recipient will attempt delivery rather than being suppressed.

Please note, however, that if there is still an issue with the recipient's mailbox or if the email address is invalid, the delivery will fail and the address will be added to the Suppressions once again.  In such a case, the recipient will need to address the underlying problem concerning the mailbox with their email host so that future delivery can be successful.  Alternatively, if the mailbox simply doesn't exist, do not remove the email address from the Suppressions.

Finally, to read more about Suppressions, please see this related help article.  If you have any questions, please open a Support ticket via the Support option of your Mailgun control panel - our team will be happy to assist!