I found this thread while searching for A Folk Song a Day (AFSAD). I am a big user of RSS feeds, and use it to access AFSAD every day (it's being repeated), so I took a look at what's on offer here.

There appear to be two RSS feeds for Mudcat:
http://feeds.feedburner.com/mudcat
http://feeds.feedburner.com/mudcat2

Their formats are very slightly different, and the first one contains more articles than the second. They're both entitled 'Feed of Topics' but they aren't - they're a feed of posts. I didn't find any reference to these feeds on mudcat; perhaps they've been abandoned.

Both 'work' in the sense that they retrieve data about recent posts. But neither is useful because they do not contain any text from the post. That is not invalid, but renders them pointless; you have to click through to the website so you might as well start there. Worse, the links within the articles point not to the post but to the thread so you can't read the post in one click. I don't know whether any of that is by design.

I'm not sure whether RSS is a useful medium for mudcat. A feed of new threads would be more useful than one of new posts IMO, provided it included the OP text.