The wiki entry for setting up a master user http://www.iredmail.org/wiki/index.php? … aster.User mentions that it is now a simple process. However, it recommends using htpasswd to generate the password file. This produces either insecure, or incompatible hashes for dovecot.
However, one can generate secure, salted SSHA512 hashes with doveadm as per http://wiki2.dovecot.org/Authentication/PasswordSchemes :
doveadm pw -s SSHA512
This can then be used in the dovecot-master-users-password, e.g.
echo -n "username:" >> dovecot-master-users-password && doveadm pw -s SSHA512 >> dovecot-master-users-password
Remembering the colon after the username, or constructing the entry in the password file yourself after running `doveadm pw`.