I needed this a few years ago badly. I ended up forwarding all email to my gmail. Then... And this is considered excessive by some... I forwarded all those to

I needed this a few years ago badly. I ended up forwarding all email to my gmail. Then... And this is considered excessive by some... I forwarded all those to a MobileMe account and check it all in Apple Mail. It automatically detects what email address my email came to and when I reply that's the email it will show from. Works great and haven't changed my setup since. From there you can create rules and whatever else you need to.