Sumitomo Mitsui Banking Corp. said Thursday it will introduce an electronic signature system on May 22 that will be used on all of the 3 million e-mail messages it sends each month in a bid to protect customers from cyberfraud.

The signature system, jointly developed by the bank and electronic signature service provider VeriSign Japan K.K., allows receivers to confirm the e-mails are authentic, the bank said. A warning sign will appear on the display if a customer receives a bogus e-mail.

SMBC said the system is highly effective in protecting customers from “phishing,” a type of fraud in which customers are lured to bogus Web sites, which often look authentic, to trick them into providing private information, such as passwords and bank account numbers.