[yobert]

Another benefit isn't a security one, but a user-friendliness one: This forces all emails to your users to be initiated by them in some way, which limits future business decisions about sending email by automated processes. Good for users, but may be bad for business.

[sroussey]

Also, possibly illegal. If you have a data breach, you must contact your users.

Probably better to use encryption with public / private keys.