No built-in, automated way no. As with all email options it is for the user to opt in to receive them – which is how it should be these days of course.

I am a little confused…  when a new user is created or registers, the default for the receive email for pm is set to true…  but as Andy says, if they choose not to receive email, there is not a way for you to force it back…  it is there option of course…

you could use a filter if you wanted to remove the option from the profile…