[thayne]

I was expecting another section about all the other ways a corporate firewall can cause issues. Not all firewalls will give you a 403. Sometimes it will be a 200 with the error in the body. Sometimes you'll just never get a response at all. Sometimes you will get an SSL certificate error, because the error response is signed using the certificate for the firewall vendor's domain instead of yours. And etc.

[ValCanBuild]

Oh god - I hope I don't have to write a follow-up to this. There's probably a bunch of hidden other firewalls I don't handle but most often I've found 403 and 503 to be the most common.