How do I enable pre-authentication and generate a PreAuthKey in Zimbra?

Pre-authentication is disabled by default. To enable it, run the command `/opt/zimbra/bin/zmprov generateDomainPreAuthKey <domain>` (replace `<domain>` with your Zimbra domain, e.g., `mail.test.com`). This generates a PreAuthKey that you can later retrieve with `zmprov gd <domain> zimbraPreAuthKey`. For a full example with sample output, refer to the pre-authentication section in the Zimbra SOAP API Development Guide 6 - Pre-authentication.