For your first question, what you are looking for is called “MasterUser” in the IMAP mail server (dovecot) docs.
Follow the above instructions to create your master user & password file.
I added the conf stuff (“auth_master_user_sepa…”) to this file:
/etc/dovecot/conf.d/99-local-masterauth.conf
Then in order to integrate it easily into the web on roundcube use this older but functioning plugin:
I have tried it and it works well for my needs. Make sure the password is super hard and long and does not get out!
- Matt