Need a Rule for 2 users that flag each other

Hi. If this isn't the right place to post this, please let me know.

On my site, users can flag each other. When 2 users flag each other, a match is made. I would like to be able to use Rules to send an email to both users when a match happens. I'm having a hard time figuring out how to set up this rule. Any help/guidance/direction is much appreciated!

Thanks!