[ih] principles of the internet

[Dave Crocker]

> applications could relay (and hence need
> routing) but mail didn't do end to end error control, but check-point
> recover in FTP did.


It's worth noting that check-point restart was a later addition to FTP.  My 
impression is that it's had limited uptake.

Email later added data integrity, through MIME Content-MD5, and as a side-effect 
of content protection through PEM, PGP or S/MIME and, more recently, DKIM, if 
one is loose about the function.  It also added delivery confirmation and error 
reporting via DSN and MDN notifications.  It had non-standardized non-delivery 
notices pretty much from the start; these were later standardized.  These all 
provide a pretty good platform for developing a re-transmission mechanism, if 
the sender wishes to pursue it.

(email relaying was also a later value-added mechanism, first through Parc's 
internal conventions, UUCP such as at Berkeley and CSNet at Udel; later 
standardized through DNS MX records, but let's not go down that... path.)

d/
-- 

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net