Support Hub is a help desk solution tailored specifically for authors on Envato marketplaces, although it can by non-Envato authors too.
It allows you to create help desk and start receiving support tickets within minutes. It's fully customizable so you can apply your own style and make it match your brand. Integrations with third-party services like MailChimp and Slack allow you to provide the top-level support for as many support categories as you wish.