To help senders with this problem, Gmail has introduced several add-ins from their Labs to enhance the mailing capabilities related to the highlighted issues.
One of the add-in, worth mentioning, is “Forgotten attachment detector”. To add this feature to your Gmail account, click on the Settings link and then go to the Labs tab. Scroll down until you find the related option and enable it. As option will be enabled, it will prevents you from accidentally sending messages without the relevant attachments, prompting you anytime when you mention attaching a file in the body of email but there is no attachment was detected.