Thanks for the first-hand input, both on- and off-list. The responses
show that there is a massive problem with what Rumsfeld called the
"unknown unknowns".
That is, except for those who have total control over their clients,
people generally have no idea what legacy systems might be sending
incomplete addresses, because everything has been working smoothly
over the past 10 or more years.
I will therefore implement a mechanism that preserves historical
defaults when upgrading from an older Postfix release. It will log
a reminder until the administrator executes a documented Postfix
command that accepts the new default after freezing any affected
main.cf or master.cf default setting at its legacy default value.
This will not rely on the automatic safety-net updates made by
"postfix upgrade-configuration" because down-stream maintainers
have sometimes implemented those selectively.
The implementation will probably be a compatibility_level parameter
that is 1 for installations that pre-date this feature, that is 2
for new installations, and that is incremented by 1 for each
compatibility break. People who don't care can set this to 999999
and never hear a peep about compatibility breaks.
Wietse
