Isn't accounting not an issue unless enough is charged for message delivery?
Similarly, when is confirmation an issue? I can see the need if one is
concerned with byzantine failures, but business communication is a natural
area in which to apply end-to-end techniques. Someone's secretary may have
downloaded the document from the web site (generating the e-mail
notification), yet it's currently sitting in an "out of paper" print queue,
waiting to be printed so it can be faxed to the hotel so its recipient will
see it after trickling in from the bar in the wee hours. Less facetiously,
even if the intended recipient has read a message (or even HUA'd), the true
ACK only occurs once the requested actions are verified to have been taken or
 I was amused to read an accounting book from the 19th century. Postage
between agents was broken out under its own head, but all the accounts for a
merchant ship were summed together at that level. The relative costs of
postage and wages, etc. must have been substantially different from ours.
On the other hand, "A Banker's Daughter"'s _Guide to the Unprotected in
Every-day Matters Relating to Property and Income_, Macmillan and Co., London,
1864: <http://www.indiana.edu/~letrs/vwwp/anon/unprotected.html> shows that
financial matters have only changed in detail (and that the "Ready Reckoner",
&c. beat functional programmers to memoization by a a good century or so)
 > X-mailer: Microsoft Outlook 8.5, Build 4.71.2173.0
Tell me it ain't so! The Document Company (and PARC, yet) don't have a mailer
that beats the bits off whatever came on your box when you bought it?