you can turn webmail off in the panel. Goto Mail -> Webmail edit the domain you want to not have webmail and check the box that says "Disable Webmail altogether?" if you want webmail but want a different name then you can change the name in the same place.
as far as phpmyadmin coming up for mysql.domainame.com, the only thing I can think of is to answer it with another question. What would you rather have to be able to get to phpmyadmin?
this is a tagline you can't steal