[Exim] twist on virtual domains

Hi,

I've gotten virtual domains to work with the example in the
documentation however I would like to do it a little differently and I'm
not having much luck.

Currently, each local domain has a single entry in a domains dbm like:

domainA.com
domainB.com

Users are added to an alias file like:

joe@???: joe@???
*@domainA.com: frank@???
jimmy@???: jimmy@???

The problem is that each customer on the system can have multiple domains
associated with their account and a new entry for each user@domain address
would have to added to the alias file making it VERY large. Since every
account is based from our own domain (customer.ourdomain.com), I believe I
can make this much smaller by doing something like the following:

Make the domain file look like:

domainA.com: customer1.ourdomain.com
domainB.com: customer1.ourdomain.com
domainC.com: customer1.ourdomain.com
domainD.com: customer2.ourdomain.com
domainE.com: customer2.ourdomain.com
etc..

And then make the alias file look like:

joe@???: joe@???
*@customer1.ourdomain.com: frank@???
jimmy@???: jimmy@???

I want to be able to do a lookup in the domains file to get the
*.ourdomain.com domain and use that in the alias file lookup to get the
forwarding address for the customer. This would add a little bit to the
domain file but cut down considerably on the size of the alias file. Is
this possible with Exim?

Thanks,

Rick