I am not sure where Excel comes into this but the following should point the way. Change your company domain as appropriate. If there are many items in the sent folder this could take a while to run
Sub CountSent()
Dim olFolder As Folder
Dim olItem As Object
Dim lngCount As Long: lngCount = 0
Set olFolder = Session.GetDefaultFolder(olFolderSentMail)
For Each olItem In olFolder.items
If TypeName(olItem) = "MailItem" Then
If Not olItem.Recipients(1).Address Like "*@yourcompanydomain.com" Then
lngCount = lngCount + 1
End If
End If
DoEvents
Next olItem
MsgBox lngCount & " items sent"
lbl_Exit:
Set olFolder = Nothing
Set olItem = Nothing
Exit Sub
End Sub