Mail API - Ticket creation with priority

Is there a way to have a tag within an email, that would set the priority of the ticket, when it is first created?  I know that you can use #priority tag within the body to set it once the ticket has been created.  However I need it when it is first created by an end-user.

Basically I wish to have an urgent tag that clients can add to their email (after hours) if something is critical.  Im trying to create a basic after-hours mechanism that will only notify the engineers if something is at the highest priority.