Running post-install calls a Debian specific script that just exits with
something that looks like an error:

| E: This is internal script used by postfix

Control: tag -1 + moreinfo unreproducible

I've no idea how do you install postfix or which post-install
script do you mean.  The postfix.postinst script does not run
other scripts.  There is a script which is used to configure
chroot jail for a given instance, - it is run internally by
postfix, and when run directly from command line, it really
produces this error message.  This is not done by any post-
install scripts in postfix as far as I know.  And mind you,
there are many systems with installed postfix 3.10.x, -- either
new or upgraded - which installed successfully.  Also,
piuparts tests are run successfully too.

So I can't do anything with this bug report unless you provide
a way to reproduce this.

Thanks,

/mjt