Abstract: A system and method are disclosed for performing the functions of administering a set of email mailboxes and executing requests by email users to transfer email messages between the email computer system and a foreign email system via established gateways. Rather than restrict an email address to the relatively static user account name, a proxy list associated with the mailbox for a particular account stores an extensible set of proxy addresses. A message will be delivered to a mailbox wherein any one of the proxy addresses matches the destination address for a given address type. A mailbox may have multiple proxy addresses for a same address type. When a message is sent to a foreign system, the originator address corresponds to a primary proxy address of the address type corresponding to a gateway used to transmit the message to the foreign system.