SMTP Service Extension for Checkpoint/Restart (RFC1845)
Original Publication Date: 1995-Sep-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
D. Crocker: AUTHOR [+3]
This memo defines an extension to the SMTP service whereby an interrupted SMTP transaction can be restarted at a later time without having to repeat all of the commands and message content sent prior to the interruption.
Network Working Group D. Crocker
Request For Comments: 1845 Brandenburg Consulting
Category: Experimental N. Freed
Innosoft International, Inc.
A. Cargille, WG Chair
SMTP Service Extension
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. This memo does not specify an Internet standard of any
kind. Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
This memo defines an extension to the SMTP service whereby an
interrupted SMTP transaction can be restarted at a later time without
having to repeat all of the commands and message content sent prior
to the interruption.
Although SMTP is widely and robustly deployed, various extensions
have been requested by parts of the Internet community. In
particular, when dealing with very large messages over less reliable
connections it is possible for substantial resources to be consumed
by repeated unsuccessful attempts to transmit the message in its
entirety. The original SMTP specification  does not provide any
means to pick up a partially completed transaction after the
underlying TCP connection has been broken and reestablished.
This memo provides a facility by which a client can uniquely identify
a particular SMTP transaction. The server then stores this
identifying information along with all the information it receives as
the transaction proceeds. If the transaction is interrupted during
the data transfer phase the SMTP client may establish a new SMTP
session at a later time and ask the server to continue the
transaction from the point where the server lost its connection with
the client. The server then reestablishes the transaction context and
tells the client where to resume operations. If this is acceptable
the client resumes operations at this point.
This extension may also be used to work around the common timeout
problem where a client times out waiting for a response from the
server acknowledging that the message has been accepted. However, use
of this extension is not an acceptable substitute for proper setting
of timeout parameters.
2. Framework for the Checkpointing Extension
The checkpointing extension is laid out as follows:
(1) the name of the SMTP service extension defined here is
(2) the EHLO keyword value associated with the extension is
(3) no parameter is used with the CHECKPOINT EHLO keyword;
(4) one optional parameter using the keyword TRANSID is
added to the MAIL FROM command. The value associated
with this parameter...