Abstract: A monitoring system is described which monitors the effect of down time of an e-mail server (2) to the disruption of communication between a client computer (1) and a remote computer (7). The monitoring is achieved through the presence of a monitor program (22) which detects that an e-mail server (2) is not functioning properly and then causes messages to be re-routed via a backup e-mail system (3-1 . . . 3-n). The backup e-mail system (3-1 . . . 3-n) sends statistics indicating the volume of e-mail received to a central monitoring system (8) which enables data indicative of the extent to which failure of the e-mail server (2) effects communication of the client computer (1) to be identified.