"Did you get that file I sent you?"
"Yes"
"Great, thanks"
$ ssh personal.sircmpwn.com rm /var/html/foobar.png
I often do this and found that I often forget about it and it turns into a big mess of outdated file, so I periodically run a script in crontab that kills files older than a certain age. Works great for me.
Next version I'll add the possibility to add a timespan in number of days or number of downloads before deletion. What about that?
I'd personally love a website that offered self-destructing url pointers or downloads. So, a url that redirects once to the target, that sort of thing.
You might not want to be too strict about it. I know I'll sometimes look at an attachment on the go, but not be able to download it until later when I'm at home.