Another important option is the `default_process_limit` (defaults to `100`). If high-security mode is enabled you'll need to make sure this count is higher than the maximum number of users that can be logged in simultaneously. This limit is quickly reached if users connect to the mail server with multiple end devices.
For major configuration changes it’s best to override the `dovecot` configuration files. For each configuration file you want to override, add a list entry under the `volumes:` key.