Is there an option to allow users to view cases created by their colleagues? In other words, if email@example.com opens a ticket but later goes on vacation, can firstname.lastname@example.org be able to see the ticket and update it?
If this is possible, can it also be permitted on an account-by-account basis? Customer account ABC may want this but customer account XYZ may not.
I think the trick is similar to what one did for high volume portal users.
You can create a Sharing Set but instead of enabling access based on the Case Contact lookup, make the Case Account lookup the criteria driver.
Assuming your customer’s colleagues are properly listed under the same Account, this would enable them to view each other’s cases.
As for doing this on an Account-by-Account basis, you would have two different Sharing Sets and two profiles. One you configure access by Contact lookup. The other has access by Account lookup.
Then you can assign different profiles to the users as appropriate.