I realise this is an old thread, but it's probably better to reply here than to start a new one!

When users join a site they can choose whether or not to opt in to email notifications. This includes emails sent by admins directly from the admin pages of the site, as well as notifications of new content, such as forum posts or noticeboard/weblog entries.

I have now added the ability for administrators to change the opt-in status for their members.

Note that you must ensure that you have the user's permission to do this (e.g., you have asked them in person)

Thanks

Joe