Great, I sent them this message:
Hi, I run NewsBlur, and a couple of my users alerted me about your RSS feed not working in NewsBlur. We’re getting a 406 HTTP status code, which is not something I’ve encountered before. I assume NewsBlur is being blocked because it’s fetching too often. However, we’re fetching every few minutes and if our feed fetchers see a 429, we back off and fetch less frequently.
If you like, here is a list of our IP addresses that you can whitelist: https://www.newsblur.com/api/ip_addresses/
Thanks!
Sam