Outlook does not use that moniker in the To: field. Some email programs do
that whenever you use the BCC field to hide the recipient names.
You can certainly use the BCC field in Outlook to do the same thing.

Signature
Russ Valentine
[MVP-Outlook]
> I've received emails with "Undisclosed recipients" in the TO: line so that
> I
> don't know who else the same email went to. Is "Undisclosed recipients"
> done
> in the form of a distribution list or what?