The compatibility_level mechanism

The compatibility_level mechanism is an excellent and very well designed
idea.  But I must have misunderstood something - or there is an error.

Around christmas I upgraded from postfix 2.11 to 3.1.6 (Debian 9).

I let the system run with compatibility_level=0 for a couple of months.

I then checked the log file for occurrences of "using
backwards-compatible", which I thought would tell me where I depended on
obsolete default settings.

Apart from some "chroot=y" warnings (which I fixed), there were no such

So I recently set compatibility_level to 2.

Very soon after that I saw the following error (with domain names changed):

This was a message sent from a local CGI script using sendmail.  Its
sender and recipient were in US-ASCII, but the subject line contained
(unencoded, standards-violating) ISO 8859-1 characters.

[]:10027 is amavisd-new 2.10.1, which I believe should support
SMTPUTF8 (see!topic/mailing.postfix.users/rKdbrpw0nc8).
But that is not a postfix issue, so forget that.

What I do not understand, postfix-wise, is that I have seen no warnings
about "using backwards-compatible" default value of smtputf8_enable
during the period where I was using compatibility_level=0.  The same CGI
script has undoubtedby sent several mails with ISO-8859-1 subject lines
during that period.

I have of course now set smtputf8_enable=no until I understand what is
going on, but I would like to understand why the compatibility_level
mechanism did not warn me about this problem.

Jesper Dybdal