ForgetMeNot is a great Mail.app plug-in that will scan each email's text in order to find words that indicate that the message should contain attached files.
If you try to send the respective emails without attached files it will display a reminder.
ForgetMeNot includes predefined languages and keywords, but the user can easily add new ones.
· Language Packs are not editable.
· You cannot make custom attachment keywords.
· Nag screen.
What's New in This Release: [ read full changelog ]
· Mac OS X 10.8.4 compatible