First of all, thank you for purchasing out asset.
I'm afraid WebGL is not one of UTMail's supported platforms. As the asset's page states, the supported platforms are:
macOS
Windows
Windows Store (Windows Phone 8.1, Windows 8.1/10, Universal 8.1, Universal 10)
Hello I bought the assets utmail and it doesn't work in my webgl project is there any way to do it?