It does seem like emails are a good fit for encryption. I can't see wanting to do anything more than simple equality checks.
For instance, all @gmail, all @yahoo, all @aol.
Maybe you want to do the cool "hey we noticed your email on haveibeenpwnd, you should change you password here just in case". In which case, anything other than plain text could prevent that from happening.
Hashing an email in that sense gets much more difficult, no?
(That's not a negative as to this blog, it's really good and I've recommended it to multiple clients already, but that level of acumen should already be assumed at that scale. If you don't have it, this blog post is insufficient.)