Update Ticket by e-mail

Hello,

I have to build the following flow:

1. requester open a ticket
2. First level take in charge the ticket and scale it to second level if cannot work it
3. second level manage the ticket or scale it to an external entity if cannot work it
4. second level resolve and close.

At point 3, I create a Status called "Escalation" that freeze the time and wait for external work (provider group has the ownership, like HP, IBM and so on), this status generate an e-mail to external entity.
Is it possibile when the external group has resolved the issue modify the ticket status from "Escalation" to "Resolved" from an e-mail ?

Thanks in advanced