Thanks to Christophe I found out yesterday that there were some problems with the feed. (Some?) people who got it through email were confronted with an error (filename not specified).
I use feedburner to redirect, measure and improve the feeds. I saw that the error was produced through content that feedburner adds to my feeds (my logo and links to social media). So, I decided to leave this out for now.
A mistake was made by me also. By copying content into the blog, I lost part of the path of some links. I removed the broken links now, and I'll be more careful next time.
Since this is a very young site (the first post is from 12/12, that's 19 days ago, not even 3 weeks...), I will run into trouble again. But because I want the content to be relevant, the links to work, and everything else to be OK in order to grow towards a professional website, I really appreciate your feedback. So, thank you again, Christophe.