The Gmail web interface prompts you to add an attachment if you mention one in the body of your message but don't attach one to the email.
Using the Forgotten Attachment Detector in Gmail
If you want to receive a notification from Gmail when you promise to attach a file to your message but don't attach any files, you can include the following sentences in the body of your message:
That’s it — no special settings or configurations. Gmail parses the messages and automatically flags when you’ve used a magic phrase without a file attachment.
We've put together a step-by-step guide for you on how to send attachments with Gmail, in case you need a refresher.
