Note that this is a hidden BCC. The user will see a blank BCC field in the compose window. If the user needs the option to remove the automatic BCC, you can futz around with custom forms - but good luck with that.
- Tools > Macro > Visual Basic Editor
- Expand project to find "ThisOutlookSession".
- Choose "Application" in the first drop-down, "ItemSend" in the second.
- Between the Private Sub and End Sub lines, paste the following code, then save.
Dim objRecip As RecipientCredit to mkizer.
Dim strBcc As String
On Error Resume Next
' #### CHANGE THE EMAIL ADDRESS BELOW ####
strBcc = "firstname.lastname@example.org"
Set objRecip = Item.Recipients.Add(strBcc)
objRecip.Type = olBCC
Set objRecip = Nothing