Re: Resuming a failed mail transfer

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There was a proposal for SMTP Message Restart in the mid-2000s (2005~2007)

SMTP service extensions for transaction
checkpointingdraft-fanf-smtp-rfc1845bis
"This memo describes the SMTP service extension for checkpoint/resume,
which allows a client to recover from a lost connection to the server
without having to repeat all of the commands and message content sent prior
to the interruption, and with less risk of duplicated messages. It also
includes an updated specification of the predecessor SMTP service extension
for checkpoint/restart."

It was not implemented in PostFix because of the following reasons (from
Wietse Venema - Postfix author):
http://www.textndata.com/forums/rfc-1845-a-175069.html
- denial of service attack (as mentioned in previous PLUG message)
- too much complexity on SMTP server as messages become transactions that
need to be tracked:
   - IP of sender (so receiver knows if restart is valid)
   - Timers that decide when a connection was broken and when to resume
   - Resumption Byte-offset per message

Ambo

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<div dir=3D"ltr"><div><div><div><div><div><div><br>There was a proposal for=
 SMTP Message Restart in the mid-2000s (2005~2007)<br></div><div><br>SMTP s=
ervice extensions for transaction checkpointingdraft-fanf-smtp-rfc1845bis<b=
r>&quot;This memo describes the SMTP service extension for
    checkpoint/resume, which allows a client to recover from a lost
    connection to the server without having to repeat all of the
    commands and message content sent prior to the interruption, and
    with less risk of duplicated messages. It also includes an
    updated specification of the predecessor SMTP service extension
    for checkpoint/restart.&quot;<br><br></div>It was not implemented in Po=
stFix because of the following reasons (from Wietse Venema - Postfix author=
):<br><a href=3D"http://www.textndata.com/forums/rfc-1845-a-175069.html">ht=
tp://www.textndata.com/forums/rfc-1845-a-175069.html</a><br></div>- denial =
of service attack (as mentioned in previous PLUG message)<br></div>- too mu=
ch complexity on SMTP server as messages become transactions that need to b=
e tracked:<br></div>=C2=A0=C2=A0 - IP of sender (so receiver knows if resta=
rt is valid)<br></div>=C2=A0=C2=A0 - Timers that decide when a connection w=
as broken and when to resume<br></div>=C2=A0=C2=A0 - Resumption Byte-offset=
 per message <br><div><div><div><div><div><div><div><div><br></div><div>Amb=
o<br></div><div><br></div></div></div></div></div></div></div></div></div>

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