auto reply framework

I'm working on the design of a program for sending automatic messages to users, based on certain conditions. It seems like there should be some sort of framework for this sort of thing, but I'm not sure what it would be called, besides "auto-reply framework." I didn't find anything when searching for that. Here's an example of what I'm talking about: Message M0 should be sent to - all current users of service S - where membership expiration is in 30 days from today Message M1 should be sent to - all current users of service S - where membership level == "premium" - where signup date was 45 days ago Message M2 should be sent to - former users of service S - where membership expiration was at least 30 days ago Message M3 should be sent to - former users of service S - where membership expiration was at least 60 days ago - where user already got message M2 at least 30 days ago Etc. Etc. So the point is that I need to be able to set up rules for what each message contains, and when each message should be sent, based on selected conditions. Is there anything out there (PHP/Mysql solution preferably) that might give some help with something like this? Thanks, Nate