A method involves blocking unsolicited e-mail being transmitted from a remote server when a roaming customer of the ISP logs onto the Internet through the foreign NAS. The roaming customer first logs onto the ISP through the foreign NAS by providing a user identification (USERID) and password, which are sent to the ISP. The ISP uses the USERID and the password to authenticate the roaming customer as a valid subscriber of the ISP. An IP address is assigned by the foreign NAS to the roaming customer and is dynamically added to a pool of IP addresses used by the mail server. The roaming customer can then log onto the mail server to send and receive email messages. Once the roaming customer terminates the session, the IP address assigned to the roaming customer is removed from the pool of valid IP address that can be used to access the mail server.