Sending "real" mass private messages

[emailapphost]

When I send mass messages to all my uses I believe this is done differently than when a private message is sent from one user to another.

Probably there is a script that writes the mass messages differently.

I now want to send "real" mass private messages to all my users - in the same way as one-on-one messages are sent.

This is because I use a Facebook plugin, that gives Facebook users alerts INSIDE FACEBOOK whenever there is a new private message to them in my forum.
But this only works when messages are sent one-on-one. When mass messages are sent, somehow it skips the Facebook connection.

Is there a way to send "real" mass messages to all users?

Thank you.