The URL for the RSS feed of all forums is here: 

  https://forum.cs.umd.edu/external.php?type=rss2

The URL for an RSS feed of just CMSC 723 is here: 

  https://forum.cs.umd.edu/external.php?type=rss2&forumids=78

You can add additional forums to a single feed by adding the forumids
as a comma-delimited list of forumids, but you'll probably want to
subscribe to each as a separate feed.  The forumid can be gleaned from
the URL of each forum.

  https://forum.cs.umd.edu/external.php?type=rss2&forumids=78,77