1) The package with Debian 9 is 3.0, … it chokes on PHP7;
2) Downloaded 3.2.1 from SourceForge (package in /usr/src);
3) Attempted to install, required removal of root mysql PW;
4) Installed and configured, encountered a weird problem:
mysqldump: Couldn't execute 'SHOW FUNCTION STATUS WHERE Db = 'postfixadmin'': Column count of mysql.proc is wrong. Expected 20, found 16. The table is probably corrupted (1805)
5) Edited config.inc.php and changed dbtype from mysql to mysqli.
6) Completed installation using postfix admin for table, .. but then granted the postfixadmin user privileges to postfix.* (the OLD database was postfix); did the repair in setup.php and now running with the old data!