Most methods provided my MailBox accept various arguments. For instance, an address field which is added to a header may be a single value or an array of values. Each value can be a string, a Mail::Address object, a Mail::Indentity object, an User::Identity object, or any other object which stringifies into valid data for an address field. Mail::Message::Field::Address and Mail::Message::Field::AddrGroup objects are also correct. It is nearly too much to chose from.