If you added PagerDuty to incident.io, you probably realised all escalations appear to be sent by the same user. Unfortunately, we currently don't have a way to change the sender of the email: due to a limitation of the PagerDuty API, all escalations will originate from the email of the user that connected PagerDuty to your incident.io account.
When you create an incident, it must always be associated with the email of a valid PagerDuty user, as bots (i.e., us) are not allowed to create incidents on their own.
If you'd rather not have incidents attached to a user's email, you could create a dedicated account in PagerDuty and connect that to incident.io. However, be aware PagerDuty will charge you for the extra seat.