Recently I moved mailing system from send mail to qmail..
After that I find the problem that the users available in Internet (I.e-Using service provider Server) are receiving the mail twice.
In Qmail my mailing architecture is like this. My mx is hosted by a service provider. I am having 30 email accounts & a catchall account in that server.
In my local server I am having 500 users.
The outside mails are delivered to internal server Catchall...