# File lib/rmail/header.rb, line 606
    def set_boundary(boundary)
      params = params_quoted('content-type')
      params ||= {}
      params['boundary'] = boundary
      content_type = content_type()
      content_type ||= "multipart/mixed"
      delete('Content-Type')
      add('Content-Type', content_type, nil, params)
    end