RE: Activation points and callout modes

On Wed, 2 Feb 2005, Martin Stecher wrote:

> > I'd not thought that the OPES processor would be maintaining queues, [...]
>
> And I assumed that most MTAs maintain something like queues in order to
> store the messages they receive before they forward them (or maybe to store
> if they cannot forward immediatly).
> But I may be wrong.

It's practially required by the SMTP architecture. See RFC 2821 section
4.5.4.1 Sending Strategy.

> Has anybody a clear view on how many MTAs (percent of real world deployment)
> can only work in a non-storing proxy mode (only accepting a message if they
> already successfully forwarded to the next MTA in a parallel SMTP dialog)?

I doubt any proper MTAs work in this way, but some firewalls implement
SMTP proxies (pejoratively known as "SMTP fux-up mode" because of the
gratuitous incompetence of many implementations). These are probably in
the target area for OPES.

> And how many try a direct forward and store only if that does not work out?

I don't think there are any. That would imply attempting to do a
complete delivery of the message to its next hop in the time between
CRLF.CRLF and its response, which is against the following text from RFCs
1123 and 2821:

   To avoid receiving duplicate messages as the result of timeouts, a
   receiver-SMTP MUST seek to minimize the time required to respond to
   the final <CRLF>.<CRLF> end of data indicator.  See RFC 1047 [28] for
   a discussion of this problem.

Tony.
-- 
f.a.n.finch  <[email protected]>  http://dotat.at/
LUNDY FASTNET IRISH SEA: NORTHWEST BACKING WEST, 3 OR 4, OCCASIONALLY 5 AT
FIRST. MAINLY FAIR. GOOD.