$ cat /etc/alpine-release
3.8.0

lxd container on Ubuntu Bionic
$ lsb_release -a
Distributor ID: Ubuntu
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic

Symptom:

$ postconf
…
postconf: warning: ldap:/etc/postfix/ldap-users.cf: unused parameter: start_tls=no
…

and many more of those.

Potential reason:

m4 preprocessor missing on build system. See these words of wisdom from the invincible Wietse:
http://postfix.1071664.n5.nabble.com/LDAP-quot-unused-parameter-start-tls-yes-quot-td91375.html

and for example this RedHat Bug Report
https://bugzilla.redhat.com/show\_bug.cgi?id=1619111

(from redmine: issue id 9422, created on 2018-09-18, closed on 2019-05-04)

• Changesets:
  • Revision 91a46ab2 on 2018-09-19T11:19:29Z:

main/postfix: Adding missing m4 build dependency

Starting with postfix 3.3 the script src/postconf/extract_cfg.sh needs m4 to successfully build.

This leads to the following log output [1] during the package build [2]:
extract_cfg.sh: line 89: m4: not found

[1]: http://build.alpinelinux.org/buildlogs/build-edge-x86_64/main/postfix/postfix-3.3.1-r0.log
[2]: https://pkgs.alpinelinux.org/package/edge/main/x86_64/postfix

fixes #9422

(cherry picked from commit aab1d5daf00c8bf56fe99ca09f0a7ea0e5216a31)