Blacklisting

Is there a button somewhere in webmail or a quick way in general to black list and white list addresses?

Nope. That’s a separate function handled by your settings at your mailboxes.example.com interface.

Why not just use the gmail platform for your email instead of DH’s

are you talking about using the gmail paid email

You can set up Gmail for your domain for free.
http://wiki.dreamhost.com/Gmail