A method and system for resolving addresses of a message including looking up, from a source directory, a group name associated with a message address of the message, looking up through a cache of user names mapped to user addresses, a user address for each of the looked up user names and returning an associated user address, and addressing the message to each looked up user addresses. Expanding group address by looking up user name in for group from source directory, looking up user address for each user name from user cache, addressing message to looked up user, address, and transmitting message to looked up user address.