My quota is working, now I have a problem with the quota warning system. Hope someone can help me out.

My machine host a few virtual user domains (eg. domain1.com domain2.com) and I would like the warnquota to send it to them instead of the default host name.

Their virtual email is working. Email for user1@domain1.com goes to user1, user2@domain2.com goes to user2
I also have the genericstable to reverse map the users.

user1 user1@domain1.com
user2 user2@domain2.com

Now the warnquota send out email to:
user@machinehostname.com (local host and machine name)
instead of:
user1@domain1.com
user2@domain2.com

Anyone have any idea how to do it?
I have search all over the place for keywords
warnquota warnquota.conf
Most of the results are for how to setup warnquota.conf which I already setup correctly and working, only the domain name mapping.

Please help.