Actually, even simpler. Just ship postmulti.service in debian postfix package, - which is just rename of the current dummy postfix.service, plus an extra line: "Alias=postfix.service", but not enable it by default. postfix-instance-generator only run when this postmulti.service is enabled. By default, ship just regular postfix.service which run `postfix start' and which conflicts with postmulti.service.
If a site needs multi-instance setup, they manually enable postmulti.service which replaces regular postfix.service with an alias for itself and enables multi-inst setup as currently done. Nothing will change in this case. And we can try to detect if multiple instances are enabled and to this in postinst. The only question I have is how to change between running postfix@-.service and postfix.service, - probably need a stop before this can happen sanely. It should be sufficiently simple and flexible. Additionally - independent of the actual schema used in this context - I think we should patch postfix-script to run configure-instance.sh where appropriate, instead of running configure-instance.sh before running `postfix start' or the like, - this way it will work for every instance no matter how this particular instance is started. /mjt
