One feature that would be incredibly handy would be the ability to email only the users that have actually participated in a certain forum(s). Some common uses:
- Sending a thank you email to all the users that have contributed feedback in your feedback/support forum in the past. You could also ask them to fill out a survey since they've prequalified themselves as the type of individuals that provide constructive feedback.
- Sending a notification to any users that have participated in forum "A" that you'll be splitting the forum into 2 distinct forums... "A" and "B", for better organization of existing and future threads.
- Sending a targeted marketing email to users that have participated in the PHP/MySQL forum since those users would likely have an interest in the revolutionary new PHP IDE being described in the email.