Embodiments of the present invention address deficiencies of the art in respect to auto-entry of addresses in an electronic message and provide a novel and non-obvious method, system and computer program product for cautious auto-entry for messaging systems. In one embodiment of the invention, a cautious auto-completion method can be provided. The method include auto-completing a messaging address provided in a messaging client; computing a similar name set (SNS) value for the auto-completed messaging address; and, posting a warning if the SNS value exceeds an SNS threshold. As used herein, an SNS includes a list of similar messaging addresses having similarities likely to result in an unintended auto-completed messaging address in a messaging system.