Summary

When a custom email stops processing email from the custom mailbox, it is likely due to the email connection. Checking at the "Connectivity Log" , it shows multiple "Rate Limited" connection status and the detail show "Could not retrieve access token for connection".

Diagnosis

1. Go to Project Settings > Email Request. 
2. Click View Logs for the affected email.
3. Click Connectivity Log and it will show as per the screenshot:

Cause

The email processor will try to pull messages from your mail server every minute, so even though it fails, it will likely connect on the next try. When the connection between Jira and the mail server fails many times, Jira no longer tries for a certain amount of time, and this time increases if it fails again. Hence you notice multiple error logs mentioning "Retrying in xxx minutes". 

This issue typically arises when OAuth fails to retrieve the appropriate access token necessary for integrating the service management project with a custom email account such as Microsoft or Google.

Solution

1. Get a screenshot of the connectivity logs. This will be handy if you want to track when the email starts failing.
2. Click on the Action menu (⋯) and select the Remove option
   1. Note: If your custom mail handler is configured as the Reply-to address, you will need to change this to a different mail handler before the remove option is available
3. To reconnect the account, click the Add external email button
4. Then, click the "Microsoft" or "Google" symbol to reconnect it using OAuth. For more information about this, refer to Switch your Microsoft and Google email accounts to OAuth documentation
5. Once reconnect, monitor the email connectivity and processing logs.