LMTP with alias addresses

[davide marchi]

Hi, my problem is this:
if i use lmtp for delivery and lookup for real_virtual_user at mydomain.com
all function perfectly and mails are delivered correctly (quota and
presence of user also)

but if i send an email to real_alias_address at mydomain.com LMTP service
(it's an alias containing several users)  dosen't find user.
How can i resolve this problem? for completeness my system users is based
on vpopmail userdb