Apparently the server is blocked.
Only with very old filters. 4 or 5 years ago one of these "filtering" companies mistakenly added our company to a "blacklist" for about 1 month because their systems are garbage. We notified them, they apologized and removed us from the list.
My advice: If they're using old filters just stop filtering altogether (because they're not up-to-date anyway).
More practical advice: add https://wyday.com and http://wyday.com to their "whitelists".