The reason Gmail's built-in filters won't work in this situation is because they can't be applied to the "X-Forwarded-For" header. That header is where the "via" domain info is stored.

My solution was to use a Google Apps Script to check my inbox every few minutes and automatically filter out messages sent via a specific domain. It actually works really well. Since implementing the script, I haven't had to deal with this type of spam at all. You can read my full walkthrough here: http://www.geektron.com/2014/01/how-to-filter-gmail-using-email-headers-and-stop-via-spam/

The quote button is inside the More formatting options menu on the formatting toolbar. When you click the arrow, a submenu pops up with a few more options, depending on the width of your window.