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

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