Spam mails from another user in my message queue

Why do i see mails from another user in my spam queue?

The e-mail has been addressed to both users.
Under the RECIPIENT column, the recipient which is listed first will be shown, this being the user to which the mail was addressed.
Further recipients can be seen by moving the cursor over the recipient's names.
Also note that it is possible, for example, user A sees the mail because he/she was included in the "cc" of the mail.
User B was addressed with "to", therefore, he/she is listed first under the RECIPIENT column.