Setting a rule on mail send on behalf of me

Hi all,

The situation is as follows:
We've got mailbox A for our department and every user has send on behalf of
rights.
When sending mail on behalf of it is important to have an updated view in
the Groupmailbox A.
For this purpose we have all users BCC the mail sent on behalf of this
mailbox to Mailbox A so we always receive a copy.

Wanted:
A rule that moves the all BCCs to a specific folder in the Mailbox A.

Tried:
Al lot of rule-settings, from "header content contains from and sender" to
"sent from {users listed} sent to Mailbox A".
Also tried to create a rule on the users client when sending the mail but
also no real satisfying results.
Either the rules don't do anything or move all mail sent to Mailbox A.

Help is very much appreciated.
--
MCDST and going for gold...