Old RSS File?

redirect them with a mod_rewrite rule that catches all requests to index.rdf and redirects them to the new feed via some 30x HTTP code.
If you don’t know what I’m talking about, give a look at the Options/Permalink page, where it shows the stuff you should put in your .htaccess; it’s basically just a bit of regex. But please be nice, put a 30x header somewhere between the client request and you sending the new feed ??

Sorry, I caught everything but the “30X” bit. I just wanted to make sure doing this wouldn’t break feed readers and all that ??

Aggregators will certainly follow a redirection, and they usually define the feed format by its content, not its extension. So don’t worry ??
And anyway, theoretically speaking, sending an HTTP status like 301 (moved) , 302 (redirect) or 303 (see other) will signal to the client that there’s some content, but that content might be different from the one requested, so you can’t say you didn’t warn them ;).
You can gently send something like:
header(‘HTTP/1.0 302 Redirect’);
before redirecting with another
header(‘Location: /mynewfeed.rss’);