Upgrade zimbra server from 8.8.15 to zimbra server 10

Based on this documentation, Zimbra supports doing a single-server in-place upgrade from either Zimbra 8.8. 15 or Zimbra 9.0. 0 to Zimbra 10, but only if you have never installed the NG modules. While supported, Zimbra is encouraging customers to instead migrate to Zimbra 10 using the Rolling Upgrade method. You'll also need a Zimbra Network Edition license before you're able to use Zimbra Daffodil (v10). If you'd like to learn more about supported upgrade paths, I've provided a direct link below:

• Supported Upgrade Paths

With any in-line upgrade they can present some unpredictable results and therefore it is usually recommended to make a backup of your server before proceeding.

Lastly, I was also able to locate Zimbra's official guide on how to upgrade to Zimbra 10 and some additional resources that may prove useful to you:

• Zimbra Daffodil (v10) Upgrade Instructions
• Upgrading from Zimbra 8.5 to 10 - Zimbra Forums