After you login to webmail you will see a screen where you cans et your default email client. You can click on the icon to select the client, or click on “Set as Default” to set it as default. Once clicked on “Set as Default” you will see a star and you will have to click on the logo to open the client.
If you already have a default client and you want to change it, click on the top right menu. A dropdown will open and you will see a star on the right side of the default client, you can click on another star to change the dafault client.