Virtual postoffice with Postfix?

Hi!

I’d like to set up a server where people can sign up for an account online and with that account get email forwarding and/or webmail access to their own mailbox. I know there’s plenty of webmail software, but I haven’t really found anything that will enable people to create their own account online.
I am looking for a solution that uses mysql & postfix.
I also want to have control over whether forwarding addresses will be created, or actual email accounts.

Who can tell me what I should use for this…?

Regards,
Evert