I just learned that att.net blocks emails from some valid domains and doesn't notify me. The emails don't even get dumped into my spam folder. Att.net just rejects them. I have no idea they've even come in.
I strongly object to ATT censoring my email. I'm an adult and am quite capable of hitting delete if there's an email I don't want. I don't need Big Brother ATT deciding what email I can and can't see.