One of the worst things you can do with email is send a message stating you have included an attachment but you forget to send it. You have to send another email with the attachment, you have just owned yourself over email. Thankfully some clever person has manged to use the undocumented API of Mail and set up a simple scanner which tells you if you have have forgot to send an email.
To install this little plugin, head over to this page scroll down and click download. Once as you have downloaded the plugin, run the install script. This simply copies the file into the correct place on your computer. It uses Terminal, dirty but it gets the job done. You need to close and re-open Mail to make sure it will load the plugin.
If all goes will you wont see anything until you try and send an email without an attachment. The plugin simply scans your email for the word “attachment”, if it finds it a small message will pop up.
It is very simple and works really well. It only scans for the word “attachment” from my little test. Try it out and see if you will use it. Hopefully it will save you the embarrassment of sending two emails.