iterate users with passwd-file passdb?

Apologies for the basic question, but I've been googling and can't figure out if this is possible or not.

Simply: Is it possible to iterate over users if I'm using the passwd-file passdb driver? Do I need a SQL-based driver if I want to iterate?

Here's what I've got right now. I don't have many users, and would prefer to retain the simplicity of the passwd-file if possible.

Thanks!

passdb { driver = passwd-file args = username_format=%u scheme=ssha512 /etc/dovecot/passwd.db deny = no master = no pass = no skip = never result_failure = continue result_internalfail = continue result_success = return-ok }

userdb { driver = static args = uid=5000 gid=5000 home=/var/mail/vmail/%d/%n }