Holds username used for logon of connected user.

A String value.  

object.Username [= value]

The Username Property syntax has these parts:

POP3 protocol specification defines that each user needs to specify his username and password combination in order to successfully access this email. Once user issues 'USER' command with username information, it is stored in this property.

You should check this value during Connected event (together with Password property) to decide if you will allow the user to access (his) mailbox or not. After you check those properties, you are free to change their values to something else. For instance, if there is more than one person checking same email, you can provide each of them with his unique username/password combination, and after successful logon just change username to 'staff' so you can reference it later easier.