It would be a great addition to have the ability to store user information in a database instead of having to add linux user accounts for everyone.
It would make WebMail more scalable. I found this for managing hundreds of users...
http://sourceforge.net/projects/dbmail Manage USers
Does anyone have any suggestions as to the best way manage hundreds of users in several domains?
jwma does support storage of userdata to an RDBMS database. Note however, that this has nothing to do with user accounts at all. It's jwma specific configuration and contact data.
jwma itself does not require that user accounts are added, nor does it require any specific authentication system. All it requires is an IMAP server (jwma authenticates against that IMAP server, it does not care how the server does it).
This means that if you need to add user accounts to your machine, that's because your IMAP server requires it, not because jwma does require it. I would suggest that you investigate some alternative IMAP server or how to configure your IMAP server to authenticate users in a way that you think scales better (LDAP, RDBMS).
Note also that jwma does not store any mail at all. It depends completely on the IMAP server to do this....thats actually what IMAP was invented for in the first place.
I think that there is a big misunderstanding in what jwma really does and I will try to explain this better in the documentation.