I had thought there was some discussion in the past about making login subsite aware. No new info would be supplied by the user, but a separate subsite or domain field would be used to create a unique user account.
If this were done, you could possibly use this domain, or some configurable domain as the default following the @. If no @ were supplied, the default would be added to the end.
However, in this case, you would still want a real email address for the user.
The main datamodel problem is that in the real world, email addresses are not unique enough to distinguish users, or even accounts. Also, users are often wary of providing a real email address until they become familiar with a site.
Maybe if users could create an account without an email, and somehow we could use the user_id cookie to remind them on occasion of the importance of providing an email address. This might include some function that would also notify the user when their email bounces (by noticing the bounced email). Email addresses are vital maintainance of user communities, and users who do not provide them are not really contributing to the community in the long term.
If the site also included a forwarding service for the local subsite account, i.e.:
tom.jackson@subsite.openacs.org --> tom@example.com
even logged in users would not be able to obtain the users real email address, but they could send them email. If this information was abused, it would be much easier to identify and handle.
