Start Workflow on Inbound Email

By default, workflows will not auto start for attachments sent to a library via email.

To enable this functionality, run the following PowerShell script on your SharePoint server.

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

$spWebService = [Microsoft.SharePoint.Administration.SPWebService]::ContentService
$spWebService.DeclarativeWorkflowAutoStartOnEmailEnabled = $true

Next, make sure your workflow is configured to start automatically when an item is created.