According to your comments, you can use a Logic App to trigger your e-mail when arriving to your mailbox, you should manager all information in field subject and then call Webhook.
Example how to trigger e-mail (it is limited to Outllok.com, O365, Gmail mails I guess)
Once you have a trigger to monitor your e-mails, you can create an Action to start it, the same logic is used to stop it, you need to create a condition when trigger your e-mail to verify subject if it contains START or STOP plus VM_NAME (something like this).
Basically an e-mail arrives (Trigger by Logic App), Logic App verifies field subject of your e-mail, according to your condition (Start VM XXX or Stop VM XXX) for subject field, you create a IF/ELSE condition, so when it trues you start it and false you stop it using HTTP request to call Webhook.
Example how to use Webook action
Create a new Logic App (Blank) and play with this, it is not so hard to understand how it works, there are a bunch of options and they are intuitive :)