What makes it particularly brutal, to me, is that the failures are typically silent. If GMail starts spamboxing my emails, I don't get feedback about that. If I'm not getting emails, I don't get feedback about that.

You can script checking those, but you'll have to re-implement it for each provider. And there are some that you can't; if I'm applying for a job, they're not going to give me an email account to test whether my stuff is deliverable.

HTTP services are absurdly easy to monitor in comparison.