Concerning external tools/apps, we don’t recommend a specific local email client for ActiveSync connections. (nor do we take any responsibility in terms of their security/privacy).
However, to continue using your Mailfence account (paying) on external tools/apps these are some of the common third-party tools/apps that you can use based on your needs:
- Thunderbird (with TBSync) for GNU/Linux, MacOS and Windows
- Bluemail for GNU/Linux, Windows, iOS and Android
- Outlook 2013 and older for MacOS and Windows
- Outlook 2016 and newer for Windows (after disabling simplified account creation)
- Nine for Android
Moreover, all the connections settings are located in your Mailfence account Settings -> Account -> My connection settings. In order, to set up a specific tool/app, please refer to the manual/user-guide of the app/tool you are using.