With dovecot, it's possible to verify passwords via LDAP with authentication binds.
I am looking for a web interface solution which features following:
The administrator creates all user accounts in LDAP and sets a preliminary password for each account. Each user should be able to change their own account password over a website with access to LDAP. So, only the password is writeable by the respective user and nothing else. The same password is used to access mail server via SMTP and IMAP and login into the website.
Note: For security reasons, it should not require a web server running on the same server as the mail server (as e.g. PostfixAdmin does).