Just to clarify, the guide says “any should work,” not “any would work”, and that’s an important distinction.
“Should” suggests that most temporary email services are expected to work, but it doesn’t guarantee universal success, some may already be blocked or filtered by Adobe’s systems.
“Would,” on the other hand, implies that every temp email provider works without exception, which simply isn’t the case.
So if one service fails, it’s just a matter of switching to another until you find one that isn’t currently blacklisted. That’s the nature of these types of workarounds, they can shift as providers adapt or as platforms tighten their restrictions.