On Jun 13, 2014, at 9:41 AM, Tony Finch <dot@xxxxxxxx> wrote: > BUT! These systems do not use the MIME external body mechanism, because it > is common for mail servers to reject these messages on the grounds that > they are too difficult to properly scan for viruses. > > The end result is something pretty simiilar to MIME external bodies, but > a complete mess from the protocol architecture point of view. Ouch. Yet another reason why a flag day may be necessary to improve the situation.