One way I see this working is to have a dedicated email address which is set up for studiometry to receive emails to scrape the
Then within PDF or HTML reports have links created mailto:x@y.com?subject=ID1092-approved-98h2r
ID which is the Studiometry Project ID
Approved - The status to be updated to - This could also be an ID opposed to a string.
98h2r - encrypted string to be sure the project id didn't get changed at some stage. A little bit of security.
Another way would be to include an encrypted string within the reply body which is set with in the email body << encyptedstringwouldgohere >> that is detected by studiometry and updates the project accordingly.
This could be handle accepting quotes, approving artwork and all types of common client tasks.