Good point.  There are two ways to do this: one way is to duplicate the test and change "instructor" to "staff".  A second way would be to add another parameter:

    Scenario: Send bulk email
    Given I am "<Role>" for a course
    When I send email to "<Recipient>"
    Then Email is sent to "<Recipient>"

    Examples:
    | Role          |  Recipient     |
    | instructor    |  myself        |
    | instructor    |  course staff  |
    | instructor    |  students, staff, and instructors  |
    | staff         |  myself        |
    | staff         |  course staff  |
    | staff         |  students, staff, and instructors  |