Spam is just one of many things that slightly reduces the reliability of email, and Bayesian filtering has reduced it to a minor nuisance. The implication that

Spam is just one of many things that slightly reduces the reliability of email, and Bayesian filtering has reduced it to a minor nuisance. The implication that email was ever completely reliable is false, there has always been a risk of mail servers going down, for example, but it was also reduced to a minor nuisance by modern redundancy techniques (for example). The implication that there even exists an actually reliable way of communication I don't think is true either, that's why email is still so widely used.