We have been warning users that Courier support would be removed since the release of ISPConfig 3.2. We are now adding a warning to the update script that Courier is deprecated. Users that see this warning will see a link to this post. I have taken the info from this forum thread on how to migrate to Dovecot. The guide is compatible with both Debian and Ubuntu. This is untested and I can't guarantee it will work. Always make sure to keep good backups so you can go back to the pre-migration state if things go wrong. These steps should be followed on the server you want to migrate from Courier to Dovecot (duh). Before starting the migration, make sure you are logged in as root user to the server. Step 1: Stop postfix and courier Run these commands: Code: systemctl stop postfix systemctl stop courier-authdaemon systemctl stop courier-imap systemctl stop courier-imap-ssl systemctl stop courier-pop systemctl stop courier-pop-ssl Step 2: Install Dovecot Install Dovecot and remove Courier with these commands: Code: apt-get -y install dovecot-imapd dovecot-pop3d dovecot-mysql dovecot-sieve dovecot-lmtpd Step 3: Change the mail daemon in ISPConfig Login to ISPConfig, then go to System > Server config > mail.example.com > Mail and set: Code: POP3/IMAP Daemon: dovecot Mailfilter Syntax: sieve And click on save. Step 4: Create a API user Login to ISPConfig and go to System -> Remote Users, and click "Add new remote user". In the form, give your new user a name and a password. I'll use example with the password examplepass. Don't use the same credentials, but create your own. The example panel will be located at https://panel.example.com:8080 with a valid SSL certificate. Enable the following functions for your remote user: Client functions Mail user functions Mail user filter functions And enable remote access for the IPv4 and IPv6 address(es) of the server you are running the script from (your mailserver). Step 5: Download and run the ISPConfig Courier to Dovecot migration script Download the ISPConfig Courier to Dovecot script: Code: cd /tmp curl https://git.ispconfig.org/ispconfig/tools/-/raw/master/courier_to_dovecot.php -o courier_to_dovecot.php Then run the script: Code: php courier_to_dovecot.php Answer the questions like so: Code: What is the username for your remote user? [example]: example What is the username for your remote user? [examplepass]: examplepass What is the hostname of your ISPConfig panel? [https://192.168.0.105:8080]: https://panel.example.com:8080 ^ without trailing slash! What is the directory where your emails are stored? [/var/vmail]: /var/vmail Don't add a trailing slash to the hostname of the ISPConfig panel. Now let the script run. This can take several minutes. Don't interrupt the script. Step 6: Run a (forced) ISPConfig update To reconfigure the services so they are correctly configured, we need to run the ISPConfig update script and let it reconfigure services. Run the script from the command line with Code: ispconfig_update.sh --force Go through the update steps. When asked whether you want to reconfigure services or not, hit enter. Step 7: Uninstall Courier Uninstall Courier with Code: apt-get -y remove courier-authdaemon That's it, you're now migrated to Dovecot!