FeedBurner is now integrated with Google and that some RSS feeds are served through a Google subdomain (feedproxy.google.com) instead of feeds.feedburner.com.
Now I syndicate my feeds through the FeedBurner MyBrand that allows publishers to use their own domains (e.g. feeds.labnol.org) instead of the default feedburner.com address.
To setup MyBrand, you need to create a new CNAME entry in the DNS records for your domain that looks something like this:
feeds CNAME feeds.feedburner.com.
The problem occurred because the CNAME settings are now different for FeedBurner feeds that have been migrated to the Google sub-domain. The new settings are:
feeds CNAME ghs.google.com.
Once I updated the DNS records, the problem got resolved and Newsgator, Bloglines, FriendFeed, etc. are again picking up the new articles. The changes were not immediate and you could see the dreaded “404 Server Error” but that lasted only for 15 minutes.
And even if you are not using FeedBurner MyBrand but your feeds have been migrated to Google servers, you may want to updated all links in your blog templates that point to the old FeedBurner address.