Here's a scenario:

A mail gets sent out to three recipients.
TO: Recipient 1
CC: Recipient 2
BC: Recipient 3

As I receive the events that the items has landed in their mailboxes, I
go to retrieve the messages. Everything is fine until I wan to retrieve
the message for recipient 3.

I see only one recipient, and that is the TO recipient. Which is normal
since he's a BC and he's not supposed to see the other recipients.

However, is it possible with soap to obtain the other recipients?

The Groupwise Web Service api on page 43 talks about filtering on
different item types. And one line specifically mentions:

to, bc, ccstring fields that are not a part of the recipient list

So my question is, is this possible to do via filters or view parameters?

Here is my view by the way:
default recipients attachments message peek