A weird one here. Running GroupWise 8.0.1 HP1 on both client (Windows XP) and server (SLES10.2). Whenever we send a HTML email that includes an embedded (not attached) image to a distribution list, the distribution list is expanded in the To: header, listing all members of the distribution list. When there are no embedded images (HTML or Plaintext) it does the right thing and includes only the distribution list itself. "Retain distribution lists on outgoing messages" is checked in our GWIA config, but this happens even when messages are sent between staff in the same post office, without even going through the GWIA, so this shouldn't have any effect anyway.

Note that the changed To: header is only apparent in the "Message Source" view, or when messages are opened with IMAP, or when the messages are forwarded outside the organisation with forwarding rules.

For example, no embedded image:

To: "IT Staff" <IT Staff.StaffPO.Staff@redlands.qld.edu.au>

With embedded images:

To: IT Staff: "Doe, John" <JohnDoe@redlands.qld.edu.au>, "Doe, Jane"

It is very easy to replicate. Just create a new HTML message, Insert a picture (not an attachment) and address it to a distribution list. Check the To: field in the "Message Source" pane of the received item. Do the same without inserting a picture, and the To: field is different.

Does anyone have any idea why this might be happening? It is a particular problem when messages to large distribution lists are forwarded externally, because not only is every address in the list revealed, but it corrupts with some recipients due to the excessively large header.