Onlooker is a friend in your outbox. It has an intelligent and customisable email content recognition system that prevents you from forgetting attachments.
When you send an email, Onlooker checks your message and looks for specific search terms like ATTACHED and then checks the number of attachments added to this email.
If you have forgotten to add your attachment then you will get a message reminding you no more looking like a fool and less wasted time re-sending the email.
The options screen (Outlook | Tools | Options | Onlooker Options) lets you choose what Onlooker looks for, so if you regularly use one of these search terms with another meaning just turn it off.
Do you have an image in your standard signature? Well Outlook counts that as an attachment, so just increase the starting count. You can turn off search terms, change the warning message and even add your own search term.