> For example, let's say that you have Postfix using a smarthost as a relay, and the new version of Postfix requires relays to have a shared secret for authenti

> For example, let's say that you have Postfix using a smarthost as a relay, and the new version of Postfix requires relays to have a shared secret for authentication with each of their trusted clients. That isn't something that can be handled by an automated config translator. This would be roughly equivalent to adding a new column or a table in a relational database with some non-NULL/empty data in it, right? Somehow we deal with this in that case, or at least we are forced to deal with it or the transaction gets aborted rather than what we have currently, which is, "oops, new postfix has been installed, you didn't read the documentation carefully, and none of your servers can send mail anymore".