You could create an addin for this (using VB6, or VSTO), or use some VBA to process incoming emails and create calendar appointments to block out the time those folks are AFK.
Something like:
Private WithEvents Items As Outlook.Items
Private Sub Application_Startup()
Dim olApp As Outlook.Application
Dim objNS As Outlook.NameSpace
Set olApp = Outlook.Application
Set objNS = olApp.GetNamespace("MAPI")
Set Items = objNS.GetDefaultFolder(olFolderInbox).Items
End Sub
Private Sub Items_ItemAdd(ByVal item As Object)
On Error Goto ErrorHandler
Dim Msg As Outlook.MailItem
If TypeName(item) = "MailItem" Then
Set Msg = item
If Msg.Subject = "OUT" Then
' create calendar appointment here
End If
If Msg.Subject = "IN" Then
' delete calendar appoinment here
End If
End If
ProgramExit:
Exit Sub
ErrorHandler:
MsgBox Err.Number & " - " & Err.Description
Resume ProgramExit
End Sub
I recommend an alternative: use the Out of Office feature. I realize the subject line will say "Out Of Office" even if you are only using the bathroom or at a meeting, but I can't imagine it's worse than what you are doing now. It's built-in and doesn't require so much effort.
ps- This is none of my business and I'll probably get flamed for asking this, but could you tell us what company that is, so I know never to work there? It sounds absolutely horrible.