When email is sent to your inbound mailbox in Postmark and fails, you will receive an Inbound Error message. The Inbound Error message is shown when Postmark could not process the email that you have sent, or it could not deliver the JSON result to your webhook URL.
A total of 10 retries will be made, with growing intervals from 1 minute to 6 hours. If all of the retries have failed, your Inbound page will show the message as Inbound Error. When making a POST request, Postmark will wait 2 minutes for a response from a server.
A common cause of Failed Inbound messages while setting up Inbound processing is a network or firewall blocking the webhook. Make sure your network accepts connections from Postmark's webhook IPs.
Postmark will display the message event type as Failed.
This can happen due to a variety of reasons. The most common ones are that destination webhook URL for email processed is not set or that the URL is unreachable.
For details about the failed message processing, you can click on the message on Activity for your Inbound Message Stream. When viewing a failed message, Postmark will list the cause for the failure.
These error messages will help you troubleshoot the issues. If you need more information about why the mail was not processed by Postmark, please contact us and we will help you diagnose the issue.
If you resolved the issue and would like to retry a failed inbound message for processing, that's possible with the Postmark API.