I’m sure it has happened to you before. Write a long email and then just hit send before adding the important attachment. Well, I usually can remember not to make the mistake but here’s a good tip that will help avoiding the follow-up email with attachment.

If you are sending an email with an attachment, add the attachment first, then compose the message, and then add email addresses to the send line. Now there’s no chance you’ll have to send the ever-popular “whoops, forgot to attach the file” follow-up.

Source: How to always remember email attachments