It’s so, so, so easy to fire off a “here’s-my-wonderful-document” email… and forget to enclose the document. So easy, and so many people do it, that there are actually plugins you can install in your email client to warn you if you’ve mentioned an attachment in an attachment-free message.
I did it again a few days ago, and whipped this up to accompany an apology to my unfortunate recipient:
Feel free to use/adapt it for your own attachment snafus.