May be that could be possible, that setting can be changed manually by admin also. That can work to send e-mail with PM to a suspended user but they can’t reply directly while suspended the system will reject if they reply by e-mail.
Wouldn’t this be only if there is already a staged user that has e-mail sending settings? If you are sending an e-mail to an address not registered that creates a new account invitation link.
There are logs of the suspension reason e-mail messages in the staff action logs, have you seen those?:
