Intellect offers the ability to add additional notes to any email message for internal use only. These notes are not sent to others if you send or forward this message to others.
They can be a great way to give yourself (or others in a shared mailbox) more detail about what might be going on than what the email can tell on its own.
If you double-click on a message, there is a Notes tab above the body of the email, just like the Notes tab found on Contacts and Events.
Type any information you wish to add. When you close the message, you'll be asked if you want to save your changes (you do!).
This help article applies to Intellect 4 or newer