Is it possible to Rebrand Roundcube as a reseller?
Afraid not. You can do it with Crossbox though. I don’t have a tutorial and I haven’t done it myself yet, which is why I don’t yet advertise it, but if you make an “admin@” email on your domain and log into it you gain some branding options. Several of my customers have already gotten ahead of me and done this. Custom domain, logo, etc.
So all I need to do is create an admin@ email and it will work?? Also would there be anyway to create some kind of single sign on with wordpress. Perhaps should crossbox in an iframe?
Correct.
You or your web developer would need to determine this. Or the developers of Crossbox may have some answers.