RFC 1845 (rfc1845) - Page 2 of 7

SMTP Service Extension for Checkpoint/Restart

RFC 1845                SMTP Checkpoint/Restart           September 1995


   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
       checkpointing;

 (2)   the EHLO keyword value associated with the extension is
       CHECKPOINT;

 (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, coupled with the name of the
       client taken from EHLO command, forms a globally unique
       value that identifies this particular transaction and
       serves to distinguish it from all others. This value is
       case-sensitive. The syntax of the value is as follows,
       using the ABNF notation of [2]:

            transid-value  ::= ""
                               ; transid-value may not be longer than
                               ; 80 characters
            transid-spec   ::= transid-local "@" transid-domain
            transid-domain ::= transid-token
            transid-local  ::= transid-token
            transid-token  ::= transid-atom *("." transid-atom)
            transid-atom   ::= 1*

       NOTE: tspecials is defined in [3]. The TRANSID is
       likely to be different from the RFC 822 message id,
       since it must uniquely identify the particular copy of
       the message being sent over this SMTP link. However,
       the syntax of transid-value is designed so that any
       TRANSID is both a legal RFC 822 msg-id as well as being
       a legal esmtp-value [4].

 (5)   The maximum length of a MAIL FROM command line is
       increased by 88 characters by the possible addition of
       the TRANSID keyword and value;



Crocker, Freed & Cargille     Experimental