There seems to be a bug in WordPress that more or less always lets the RSS feeds consist of only the 304 headers. Having not really enough time at my hands to fix this bug myself, I will have to wait until someone in the WP community finds a solution for it. It shouldn’t take that long :-) Sorry for that :-)
EDIT: Working again? … What a single post can change ;-)
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Alternatively, this website also supports Webmentions. If you write a post on a blog that supports this technique, I should get notified about your link 🙂