I've been wracking my brain over this problem. I have no idea what to do anymore.
So, my friend told me she couldn't go to stamps.com on her computer at work. I try it on my computer and I can't access that website either. However, we can access pretty much all other websites. So then I try the basic clear all caches, cookies, browsing history, etc. Still no go. I rebooted the computer (Windows 10 20H1). Still no good. I turned off the firewall. Still no good.
I then asked a friend in a different office in the building to try and he can't access the website either. They have their own Internet through the same ISP. So I think it's the website that's the problem.
But Stamps.com shows all fully operational on their status page. I then think it's the ISP problem. I
I then tried flushing the DNS. Still no go. I tried setting the DNS to Google's 8.8.8.8 and 8.8.4.4 and still no good.
I try both Edge (Chromium browser) and Internet Explorer. Still no go. Then I tried Mozilla Firefox and it works. So I thought, aha! It's a browser issue. HOWEVER, I then go to my phone and I can't access the website when connected to our WiFi or my friend's WiFi. However, if I disconnect the WiFi and connect via my mobile network, I can connect! Using the same browser!
It's driving me crazy. I don't know what to think. This site used to work on every browser we tried. The problem just started this afternoon. We also use Stamps.com through their software. However, the software cannot connect. We know their software uses Internet Explorer as their backbone.