Is there a way to reference an Excel user-defined function in Outlook VBA?
I created a Boolean function that, via a userform, accepts a username &
password & authenticates them against ActiveDirectory. The function is in an
Excel workbook & I can use it in VBA in any other Excel workbook by adding it
via Tools/References/Browse . . . in Excel VBE.
If I try to add it in Outlook VBE, it returns message, "Can't add reference
to the specified file."

Alternatively (preferably) is there somewhere else to create this function
so that it could be used in any Office application? From research, I believe
an Add-in would be ideal but I don't have Visual Studio & don't know what
other options are available.
--
Will