You were BCC'd on those messages. Sender sent the message to
himself and BCC'd you.

What about the ones received that say Undisclosed in the To box?

Same thing without the 'Sent the message to himself' part. (ie, the
To line was blank)

Tried it but I do not get a message showing To: undisclosed recipients


It depends on the sending client and mail servers, IIRC. What is it you want
to do?

--
f.h.
Microsoft Outlook MVP