Abstract: A method and apparatus for use in a computer system comprising an email system that generates and receives email messages. The email system manages a first plurality of email messages comprising at least some of the email messages generated and received by the email system. The email system also has a global address catalog that comprises information and provides an index into the first plurality of email messages. The computer system further comprises an extension system that interfaces with the email system and manages a second plurality of email messages comprising at least some of the email messages generated and received by the email system. The method comprises creating an extender catalog, for indexing into the second plurality of email messages, that comprises at least some information that is different than the information in the global address catalog.