A communication apparatus enhances security in transmitting electronic mail to a destination mail address without degrading operability. An MFP is connected to an authentication server and a mail server via a network. A user name and a password are entered in a user name entry screen. The MFP requests the authentication server to authenticate the entered user name and password. When the user name and the password are authenticated, the MFP is operable to acquire an e-mail address, a SMTP authentication user name, and a SMTP authentication password according to SMTP associated with the authenticated user name and password from the authentication server. The MFP requests the mail server to authenticate the acquired SMTP authentication user name and SMTP authentication password according to SMTP. When the SMTP authentication user name and the SMTP authentication password are authenticated, the MFP is operable to transmit an e-mail to the mail server.