If your On Premise Engine stops transmitting data to SigParser after a few months or a couple years it is often because the app secret stopped working.
Go to Microsoft Azure portal (https://portal.azure.com)
Go to App registrations
Find the SigParser application you created when originally setting up the On Premise Engine
From the menu on the left, select Certificates & secrets > Client secrets > + New client secret
Enter the following details:
Description: SigParser Mailboxes Secret 2
Expires: 24 months
Select Add
Copy and paste the Client Secret Value (NOT Secret ID) from Azure
Depending on how you setup the secrets
Find the Azure Secret store you created previously for SigParser and update the Office365ClientSecret
OR if using the secrets.json file then update the JSON property Office365ClientSecret with the secret
Next time the application runs it should work.
You can run the scheduled task manually and view the logs to make sure it is properly processing records.
It will reprocess any missed emails