So each user has its own DID? or just one DID for the whole system, server answers and you get all the faxes in one box?
If the 1st is correct see my above post.
If it is the latter it will work but what's the point of a fax server? get a fax machine.
You need a PRI integration or SIP so that after the call gets routed to the fax server it also passes along the did info, therefore the fax server knows which users inbox the fax goes to.
With analog integration you lose the did portion as it is a diffent technology not designed what you are trying to do.
Unless you map each DID to a specifig VG port.
For example DID 1234 port 1, DID 1235 port 2, etc.
So DID 1 will only get one call at a time on a specific port.
That will work but talk about hodge podge.