Logical Conditional Model Level Validation

Guys I have a model say Contacts and it has following attributes
id,email and address
Now I want to store only those tuple whose email as well as address
attributes are unique.
I have tried this one
validates_uniqueness_of :email && :address

but it doesn't work. So asking for help

It's done.
Should be written
validates_uniqueness_of :email, :scope=>:address, :message=>"your
error message"