def conventional?
      self.syntax = :invalid
      self.local =~ CONVENTIONAL_MAILBOX_REGEX or return false
      self.valid_size? or return false
      self.valid_encoding? or return false
      self.syntax = :conventional
      true
    end
def conventional?
      self.syntax = :invalid
      self.local =~ CONVENTIONAL_MAILBOX_REGEX or return false
      self.valid_size? or return false
      self.valid_encoding? or return false
      self.syntax = :conventional
      true
    end
True if the part matches the conventional format