where to setup virtual_mailbox_maps

[frakass]

Hello,

I have a domain in virtual_mailbox_domains:

aaa.com

I have also the virtual_alias_domains which include:

bbb.com

I know how to forward x at bbb.com to y at aaa.com by setting up the file
"virtual_alias_maps":

x at bbb.com y at aaa.com

(and run postmap after the changes.)

But, how can I setup virtual_mailbox_maps (if I name this correctly)? for
example, 111 at aaa.com forwards to 222 at aaa.com.

Thank you.