An email wrong transmission preventing apparatus calculates memory ratios of addresses of emails in a transmission log by a model expression in which the memory ratios decline over time, compiles the memory ratios of the emails for each destination to set weights, and records the weights in a user weight list. When receiving a planned outgoing email, the apparatus compares the weight of the destination of the planned outgoing email obtained by referring to the user weight list with a predetermined threshold and determines that the destination is “reliable” only if the weight is over the threshold. If even one of the destinations of the planned outgoing email is not “reliable”, the apparatus causes a sender terminal to display an address check screen to prompt address checking. When “checked” is inputted, the apparatus transfers the planned outgoing email to an email transmission server.