some advice needed on some coding

Hi, ok if anyone can give me some advice on the best way, much appriciated. I have a central table which stores only email addresses (for which users can add to by entering their email address on a "sign up to newsletter" form. Some of those email would already exist in my orders table for any user who have previously placed an order...and/or the email address would already exist in the user table (in case a user has registered on the website but not placed an order yet).

I had created a simple email marketing campaign manager into my website, now what I would like to do is allow the client to be able to create email groups based on certain critieria they select (be it filtering fields from the orders table or filtering fields from the user table) but with this using only the emails that are stored in the central table which stores emails (so lots of cross-checking involved).

Now just need to best approach to this...I was think of creating another tables in the database which will store temporary data from the criteria mentions..this table could be called something like EmailGroups so it be used for creating groups. then this table would be used in the WebAssist Email Server Behaviour.

Any thoughts or tips much appriciated :)

Chris