class Mail::Address

def display_name=( str )

a.format #=> 'Mikel Lindsaar '
a.display_name = 'Mikel Lindsaar'
a.address = 'mikel@test.lindsaar.net'
a = Address.new

Provides a way to assign a display name to an already made Mail::Address object. 
def display_name=( str )
  @display_name = str.nil? ? nil : str.dup # in case frozen
end