Hi,
so not much to do on the qmail side. and thats the reason everything user related is done in dovecot itself.
ok
...but if nobody knows if its possible inside the dovecot lookup process, a new/seperate lookup process that calls dovecot-lda with the username instead of the mailaddress might be the only opportunity.
As I understand the original problem, you need one mail to be delivered to several users, which means you need to figure out how to alias or forward. Steffen's approach is a super good idea I intend to stuff into my back pocket, and is probably worth pursuing given your usage case.
Other than that, and based on what I know, I would still be inclined to try and solve this by creating a local user and configuring a .qmail file to forward the mails to AD users, but tweaking your defaultdelivery to accommodate a per-user .qmail file might be tricky or impossible in your situation. A global sieve script might be another approach to forwarding mails from a virtual address to valid users, but I haven't implemented one, so I can't say if it fits your situation or provide advice on configuring one. Another approach could be setting up a mailing list, where the list address is the common address that delivers to subscribed users. Perhaps delivery to a single user and a shared folder might provide a usable end result as well...
Whatever you end up doing, I am interested to hear what works for you in the end...
Greetz Matze