Inbound Mail Gateway

Good afternoon,

I am researching a central inbound mail gateway. I am looking for a way to have mail bound for 6 separate domain names hit a central point and be forwarded from there.

Example:

mike@dog.com
mike@cat.dog.com
Mike@bird.dog.com

Change MX records to point to a server called
mail.dog.com

From their it then forwards the messages to the appropriate server.
cat.dog.com, etc.

The idea is that when I can have a central email server with a common name space. So if auser want to have a dept email server they don't have to change their business cards or publications. Also when I retire a server the email from cat.dog.com still is received and forwarded.

I have heard sendmail and postfix can do this but I am looking for a good how to?