Re: is SMTP a candidate for OPES ?

At 14:01 06/07/04 -0600, Alex Rousskov wrote:
>The above "you do not know" assertion is false for some kinds of
>e-mail transformations (e.g., detecting a known spam by looking at
>Subject lines or headers) and true for some kinds of HTTP
>transformations (e.g., detecting a virus by examining sensitive octets
>at the end of an HTTP entity).
>
>Overall, there is nothing special about SMTP here, IMO: some OPES
>adaptations require the whole message, some do not. Sometimes OPES
>processing overheads delay the entire message; sometimes they delay a
>portion of the message.
>
>Why is SMTP special at this level of thinking?

(Trying to answer this question, without making any statement about OPES 
applicabiluty...)

The delivery requirements associated with SMTP effectively require a mail 
relay to store an entire message until it has been successfully transferred 
to the next relay.  This is more than just "best effort" delivery -- I have 
seen the term "heroic effort" applied here.  A message is expected to 
survive a complete restart of an MTA system while an SMTP transaction is 
in-progress.

It's true that the spec doesn't actually say that messages must be stored, 
but that does seem to be a consequence of the responsibility that the spec 
places on MTAs.

In practice, I think this means that most real-world MTAs do store messages 
in a non-volatile message store, where they might arguably (I won't say 
"reasonably") be regarded as not in-transit.

#g


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Graham Klyne
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