ietf-openproxy
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RE: [draft-ietf-opes-smtp-use-cases-01]

2005-01-22 00:13:47

I think you are rejecting a reasonable response modification scenario
by saying "implement your service another way."  I don't see any
reason to exclude having the response modification done "in the flow".

Hilarie

On Fri, 21 Jan 2005 at 22:28:29 +0100 Martin Stecher said:
 Hi Tony,

 > >
 > > I do not see any use case that deals with response 
 > modification. Does
 > > anybody see a use case in which first the MTA should check for the
 > > response of its peer and then forward that response to the callout
 > > server for further modification? What can be modified here? 
 > Responses
 > > are only short acknowledgements or error codes. So turning 
 > an ok into an
 > > error would be possible but the callout server does not 
 > really need to
 > > see the ok first, does it?
 > 
 > There are some situations in which an SMTP server may wish to 
 > call forward
 > to another server in order to validate a user's address. For example,
 > Cambridge University's central email cluster acts as the MX 
 > and anti-spam
 > and anti-virus filter for several departmental email servers. 
 > The central
 > servers do not have a list of the valid email addresses for the
 > departmental servers. In order to verify the recipient addresses on a
 > message during the SMTP conversation with a client outside 
 > the University,
 > the central server performs an abbreviated SMTP conversation with the
 > departmental server to check what response it would give to the RCPT
 > command. Success and failure responses (250 and 550) are passed to the
 > external client, but temporary failures (4xx) are modified to success
 > responses so that we take responsibility for a message if the 
 > departmental
 > server is having problems.
 > [...]

 Thank you for this real world use case.

 Not sure whether you see this as a response modification example, it's not 
IMO:
 The university's central email server can send the RCPT
 command to the callout servers that have access to the departmental
 user directories and get the reply for this command in response to its
 OCP request.
 But it is not necessary to first create a pseudo reply in the central
 mail server and to have that modified by the callout server. That
 pseudo response would have no meaning to the callout server.

 Regards
 Martin


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