RFC 1845 (rfc1845) - Page 3 of 7

SMTP Service Extension for Checkpoint/Restart

RFC 1845                SMTP Checkpoint/Restart           September 1995


 (6)   no additional SMTP verbs are defined by this extension;
       and,

 (7)   the next section specifies how support for the
       extension affects the behavior of a server and client
       SMTP.

3.  The checkpointing service extension

   When a client SMTP wishes to use checkpointing to eliminate the need
   to retransmit all message data in its entirety in the event of a
   session interruption, it first issues the EHLO command to the server
   SMTP. If the server SMTP responds with code 250 to the EHLO command,
   and the response includes the EHLO keyword value CHECKPOINT, then the
   server SMTP is indicating that it supports SMTP checkpointing and
   will honor requests to restart interrupted SMTP transactions.

   The extended MAIL command is issued by a client SMTP when it wishes
   to enable server checkpointing. The syntax for this command is
   identical to the MAIL command in [1], except that a TRANSID parameter
   must appear after the address.

   The complete syntax of this extended command is defined in [4], with
   the esmtp-keyword TRANSID and transid-value parameter as previously
   defined.

   The value associated with the TRANSID parameter must be an identifier
   that serves to uniquely identify this particular SMTP transaction.
   Only one TRANSID parameter may be used in a single MAIL command. Care
   must be used in constructing TRANSID values to simultaneously insure
   both uniqueness and the ability to reidentify interrupted
   transactions.

   The TRANSID is structured to ensure globally uniqueness without any
   additional registry. The transid-domain part should be a valid domain
   name that uniquely identifies the SMTP client. Note that this is
   usually the same as the domain name given in conjunction with the
   EHLO command, but not always. The EHLO domain name identifies the
   specific host the SMTP connection originated from, whereas the
   transid-domain may refer to a group of hosts that collectively host a
   multi-homed SMTP client. The transid-local part should be an
   identifier that distinguishes this SMTP transaction from any other
   originating from this SMTP client.

   Despite the structured nature of the TRANSID the server should treat
   the value as an opaque, case-sensitive string.





Crocker, Freed & Cargille     Experimental