The problem I was trying to solve was to support an option for different recipients, that is all. I don't think a drop down with 1 item makes much sense. I don't see a need to show a text field if there is just one either because the form title can convey the one person, recipient or purpose.
The drop down is driven by the pipe separated email address not the aliases. If there is only 1 email address it will not show a list no matter how many aliases are entered, and it will show the email addresses in the drop down if no aliases or not enough aliases are entered. Also if people want a dropdown they can enter the same email for as many aliases as they want, but it makes sense to have at least 2 items so they should enter their email twice or once per option they want in the list to create the list.