Hi Ravin,
You won't be able to do this using a standard workflow because you won't be able to parse the subject for a case number or search for the case number.
I suggest you create a Post Create plugin on the email entity. In the plugin, check that the email is an incoming email (directioncode attribute), parse the subject for a case number and query the case entity for the case and if you get a result, send an
notification email to the customer.
Michael Palmer
xRMPalmer
@MJFPalmer
Rockstar365