Forward All Email Account to one Mail Account

Hi,

I've been trying to forward all email accounts (@domainname.com) to one single subdomain account (backup@subdomain.domainname.com) with no avail. The method that I've tried so far :

1. Using domain forwarders which is weird why it doesn't accept domain forwarding to a single email account just like the old days cPanel used to be :|
2. Using Catch-All which means only unrouted email will go to the address, which is not a feasible method since I need to have both accounts to save the incoming mail.
3. Using the highly unlikely domain filtering in which it does have a better priority over forwarding aka : I can't save the mail sent to the accounts at domainname.com

The only working method is to set-up each and every account on domainname.com manually to forward to backup@subdomain.domainname.com which is not practical in a sense that I have at least 150 email accounts.

Is there in any way that I can set-up the forwarding for the above case ?