Forgot to attach the file?

Nice. That will be annoying, hopefully, and it's so easily done. Haha! When they refer to it later, they will find the attachment missing. Excellent! If it's late enough they will bring their laptop to a crucial meeting, expecting to refer to the file, only to find they haven't got a clue what's being discussed.

Here's how to make it more annoying, especially if you want to appear helpful (which is nice as you will never be blamed for doing it).

Send a supplementary email including the attachment. Don't include ANY of the information from the original, probably lengthy email. Best of all, call the follow-up something generic, like "oops".

If a message should have multiple attachments, try "forgetting" just one. Never send out the whole lot again. That would be too clean.

A bit more subtle, but it still works:

Send the whole message again, but completely Quoted (it will be blue and quite annoying in most clients, and with luck it will have random line breaks in it). Most email programs do this by default.

See how easy it is to turn email into an Aegean stable? Some further tips:

You can include the attached file anywhere in the new text. Best place is in between the bottom of the quoted text and your newly added signature. They will never look there. Tee-hee!

Again, if you have the chance, change the subject line. That will stop those oh-so-clever types who think they can use message threads to keep on top of things.

Anything you can do to multiply the number of messages the recipient has to handle, or the ambiguity of the situation, is fine. It all adds to data overload, and slows down their ability to do "good work". Some of them even think that's why they're at work!