Double mail issue

Hi

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 account.
My Fetchmail is like this-
poll (My server IP) proto pop3 localdomains mydomain.com no dns uidl
envelope "Delivered-To"
qvirtual (domain)-

user catchall@mydomain.com with pass "*****" is localcatchall@seml.co.in here keep forcecr flush dropdelivered
Configuration for the users available in service provider server.
/home/vpopmail/domains/mydomain.com/8/pushmail_online/Maildir/

Now the problem is like this-When a outside domain user sending a mail to two users I.e-one user directly receive the mail and another one receive via catchall . Now the user available in external server(MX or service provider end) recieves the mail two times, 1st time recieves directly and next is routed via local server.
Now I want to solve this double mail issue. Is there any modification needed in fetchmail?
Please have a deep look at this scenario and help me out from this situation.

Regards,
Jyotirmay