[support] Non-unique account email addresses

[Luke]

This is something of a "if that won't work" condition to my last message 
(accounts w/no email address).

If it is necessary for accounts to have email addresses, is there a way we 
could use an in-house blackhole type address for this?  Assign the same 
address to any account which does not have a real address, and let the 
user login without needing an unique address to be assigned?

I don't suppose it would be as simple as removing the key on the user.mail 
column?

Even if so, if there is a module which would enable this to survive 
upgrades, that would be good.

Luke