ExpanDrive

This is not a joke. The Gmail team has enabled an “Undo Send” feature in Gmail Labs. There’s no black magic or voodoo; it just holds onto your message for five seconds in case you want a panic take-back. After that, the email is gone and un-recallable, just like normal.

I rarely use the Gmail web interface, but I’ve thought about writing a Mail.app plugin to do this for years. I can’t count how many times I’ve tried to scramble into the “Sending…” folder and delete a message before it escapes. I’ve never once pulled it off.