In directadmin, mail can be forwarded to other mail box / e-mail address by setting forarder.
However, the setting for master account and virtual account are different. here is the tips.
For master account:
For virtual account:
The different is that for virtual e-mail forwarder, a copy must be sent to the virtual account and forward another copy to the forwarder address. However master e-mail forwarder doesn’t.