Re: [plug] Resuming a failed mail transfer

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Author: ambrosio jr berdijo
To: Philippine Linux Users' Group (PLUG) Technical Discussion List
Subject: Re: [plug] Resuming a failed mail transfer
There was a proposal for SMTP Message Restart in the mid-2000s (2005~2007)

SMTP service extensions for transaction
"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):
- 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

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