How about this for an easy to implement feature that will save hoards of people from looking like fools.
If you are composing an email that has the phrase “I’ve attached” or “Attached you’ll find” or anything that seems to imply that the composer of the email intends to attach something to the email, when they click send check whether there is indeed something attached and if not ask them if they’re sure they want to send.
Is that too MS Paperclip’ish?
Just a thought.
arbitraryuser 
This is one of the new features in Evolution 2.12 (the version released with GNOME 2.20). See http://www.gnome.org/start/2.20/notes/en/index.html#rnusers-email-and-calendar
I have some vague impression that KMail may also do this, but I’m not sure.
AFAIK, this is a planned feature for the next version of Evolution.
Thunderbird, Gmail and Evolution all have that feature. Thunderbird, you need an extension, I think. Did you google?
No, I didn’t google… Why must you hate me so.
Because Vhata is a bully.
http://www.twistermc.com/blog/2006/08/06/attachmentreminder-never-forget-attachments
j.
Kontact/Kmail has had that feature for a while already… Prompted me again the other day when I nearly sent an e-mail without an attachment.