The Requester field will accept any email address entered and it will create a ticket using that email address as the requester. It also adds the email address to the Requester drop-down list for other users to see and choose from also.
We've noticed that users are not manually entering in their personal emails but due to their browser auto-fill, sometimes the requester field will update based on other fields they are auto-filling in. We'd like to prevent this and only allow our requesters to submit tickets for themselves and others in our organization only.