A system manages computer security risks associated with message file attachments. When a user of an electronic device with a messaging client attempts to open an attachment to a message that is in the client's inbox, the system will analyze the message to determine whether the message is a legitimate message or a potentially malicious message without the need to actually process or analyze the attachment itself. If the system determines that the received message is a legitimate message, the system will permit the attachment to actuate on the client computing device. If the system determines that the received message is not or may not be a legitimate message, the system will continue preventing the attachment from actuating on the client computing device.