Comment by herbst

That's one anecdotal experience and simply not an ultimate turth.

I've had a email startup (sold meanwhile, but still running) and seen all these mentioned issues and know very well how painful this can be, but far from impossible. There is a market for clean IPs for company infrastructure, that's a thing still as well.

Probably I shouldn't say email is much better. But phone numbers definitely are a very weak decision for any kind of security.