If you are not able to setup account level email integration through forwarding, a way of each user individually recording their outbound emails with contacts through BCC'ing BeeCastle.
Firstly, you'll need know your BeeCastle email address which you'll find in the 'Admin Settings' -> 'Email Logging' menu of the BeeCastle web app. This will be in format of <acccount-specific-inbox>@inbox.beecastle.com
Then, when you want to log an email you are about to send BCC the BeeCastle email address and the email will be recorded against the recipients if they are contacts within BeeCastle. Check it worked by visiting that contacts dashboard to see if the email is logged in their interaction feed.