How to add mail to database

I am using DEVONThink ProOffice and Mountain Lion and the latest version of Mail.app. I do not have the menu entry Message>Add message to DEVONThink Pro. How do I copy any email message to my database?

go into the menu bar click on devonthink and then click on install add ons and follow dialogue box

You can also drag and drop from Mail.app into DEVONthink.