Hi,
It depends on how you have the MX record/details for "studentgroup.org" set up, and whether you have the ability within the 'holding area' for it to be configured to forward out....
If you/they are running Exchange, then you could configure it to forward all mail that hits that users mailbox to their external e-dress, and if the 'holding area' is smart enough, you may be able to configure it there instead....
Personally, I have a mail carrier that delivers all of my mail (for the 10 domain names I have) to my server that runs Exchange, but the same carrier can also be set to use individual mailboxes - as opposed to the '*@domain-name.ext' "catchall" that I use - and each mailbox can be set up separately to all of the other ones.......