Roundcube Spam Filter?
 

I use the email client via Cpanel. Roundcube, Squirrelmail and I forget what the other one is.
Anyway, with these email programs is there a way to mark the emails as spam somehow?

Round cube is just an interface so no you can't use it for anti spam purposes

I don't understand. Is Gmail not just an interface as well but they don't have a problem adding a spam filter.

Just found an email filtering option before you enter the main area. Looks like it might do the job.

gmail has a server to deal with emails spam .