Hello :)
IETF has put up an internet draft at
http://www.ietf.org/internet-drafts/draft-khanna-smtp-mail-transfer-reliabil
ity-00.txt.
This draft discusses the issue which makes the data transfer in SMTP
protocol highly vulnerable to a "resend" in case of a network
disruption. We then discuss a means by which such a "resend" can be
avoided, by transferring mail data only from the point of disruption.
As I previously pointed out in private mail, I believe a facility for this
is already defined in RFC 1845.
Ned