Substack blocking GitHub IPs

[bmos]

I've noticed that feeds that give 403 Forbidden are always Substack.
Are they blocking GitHub IPs?
The same feeds pass the validation check script when run locally on my home internet connection.

https://thethornnyc.substack.com/
https://redallover.substack.com/
https://eastbaydsanews.substack.com/
https://thenyclocal.substack.com/

[colinmahns]

If it's possible to spoof a user agent, it might resolve this issue. Could be blocking that rather than the IP, or at least determine if it's GH vs running the script

[bmos]

I ran the same code on my computer and it let it through so it's either IP, route, or combination of those with something like UA.