# File lib/action_mailer/vendor/tmail/net.rb, line 246
246:     def exec( mail, top = true )
247:       mail.mime_version = '1.0' if top
248:       mail.set_content_type 'multipart', 'mixed'
249:       e = encoding(nil)
250:       if e and not /\A(?:7bit|8bit|binary)\z/i === e
251:         raise ArgumentError,
252:               'using C.T.Encoding with multipart mail is not permitted'
253:       end
254:       mail.parts.each do |m|
255:         exec m, false if m._builtin_multipart?
256:       end
257:     end