Hello everyone.!!!
I have prepared a mail server recently. I installed postfix, dovecot & roundcube on ubuntu 20.04. I installed roundcube via apt-get install and it installed roundcube 1.4.3. In dovecote configuration (/etc/dovecot/conf.f/10-auth.conf) I have below configuration>>

disable_plaintext_auth = yes
auth_mechanisms = plain login !include
auth-passwdfile.conf.ext

In /etc/dovecot/conf.d/auth-passwdfile.conf.ext file I have below configuration:

passdb {
driver = passwd-file args = scheme=PLAIN username_format=%u
/etc/dovecot/dovecot-users}

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

And I have listed my virtual users at dovecot-users file in below format:

user@domainassword

virtual Users login/logout, sending/receiving mails are working fine through roundcube.

But I can not figure out which password driver to use and how so that my users can change their own password. It will be appreciated if you look into my issue and help me.

Thanks in advance.

it's been years since i ran a mail server, but i do remember password management issues on the dovecot side. you will need to configure dovecot to look up passwords in a database at a minimum. that or PAM. i remember being urged to make all mail users also be system users. but i didn't want to open up another security exposure. i didn't trust most of the users. in theory, someone might find my hidden ssh port. so i didn't go that way and i didn't want to use PAM. i don't remember my setup but it was some kind of database shared with postfix for outgoing submission authentication.