I have Office 2003, which includes Outlook. The file outbak.dll is on my PC located in:
C:\program files\microsoft office\office 11\addins
Perhaps the location may be different if Outlook is installed as a separate stand-alone programme, and not bundled with Office.
By the way, the file has the same date as when I installed Office about 17 months ago. I have Norton AV 2003 installed; no junk mail filter. My Outlook runs fine.
Don`t know if this information is of any help.