[TeMPOraL]

Yes. At this point it's well-known that ports 80 and 443 are the two ports no company[0] can afford to block. This means, among other things, that making your product as a webapp is by far the best approach if you want to "worm your way into" corporate environments, as any worker can use it out of the box, while anything else would require IT approval.

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[0] - Except those creating high-security environments with airgaps and whatnot, but that's a special case.

[actionfromafar]

Proxies can be pretty harsh too. Not sure if we have a whitelist or a blacklist but it’s pretty restrictive.