A single email account can have multiple addresses assigned to it, known as aliases. If you have roles on multiple campuses, each campus will have an address that routes to the same email account, so you may have addresses @unk.edu, @unl.edu, @unomaha.edu, and/or @nebraska.edu. Among them, one is set as the Primary Email Address based on your primary campus affiliation.
That primary campus email address is used as the sending address for all outgoing emails.
Your primary campus is determined by your HR roles, and if you need to update it, employees can reach out to their HR team to start that process. Students should reach out to the registrar of their primary campus.