Crelate offers the ability to track individual emails within your database now. This is a feature that is enabled by default and you can uncheck the box to disable it upon sending an email if needed. You can find the option in the bottom right corner of the pop-up email window:

You will be able to tell which emails have had this option selected by viewing the email activity in the stream. It will say "Tracked" here:

Once the recipient opens the Tracked Email, it will change to "Viewed":