Connecting with Existing Installation of mail server

[BiglifeMatt]

I already have an iRedMail server (running Roundcube though I don't use it unless needed), and an OpenLDAP server. Does this app just install an instance of Roundcube that can point to the existing external email server? I'm not sure I'm understanding how if that is what this app does or if it is more than I need for my current solution. Basically I'm just wanting to use it to replace the Nextcloud Mail app as there are some features I prefer in RC.