The present invention provides a system and method for detecting incorrect e-mail addresses in outgoing e-mail communications. In a first embodiment, a domain name database creates a table of domain names by automatically storing the domain names of e-mail addresses from which incoming e-mails are received. When a user creates an outgoing e-mail communication, the system checks the domain names provided by the user with those domain names stored in the table. If the user-provided domain name does not match any of the domain names in the table, or closely resembles a domain name in the table, the user is prompted to confirm the provided e-mail address. In a second embodiment, e-mail addresses are extracted from incoming e-mail communications and stored in a memory in a client computer e-mail communications system. The system checks the memory for the presence of the e-mail addresses provided in outgoing e-mail communications, and generates a prompt when an e-mail address is not present in the memory.