Exchange 2010 Anti-spam - Block only outgoing msgs from external users to be received from specific inside users

Hello All,
We have an exchange 2010 typical installations with many transport rules.
We have created additional mailboxes based on the departments (like departmental e-mail addresses) and when some users wants to send to outside emails they add to the From Filed in outlook the departmental address and they send the mesages, in order the emails to external parties to be send from departmental email address. Many of the outside people they reply/ send new messages to departmental email address, but there are some people that send emails to personal addresses and not to departmental. I install the anit-spam function in exchange and i used the option Recipient filtering and i added the required email personal addresses that i would like to block the emails taht are sent to these email addresses. when an outisde users send an email to a personla email address that have been added to recipient filtering, the system blocks the message (this is correct) but when an external users sends an email to departmental email address the messages passes but it did not received from internal users. I forgot to tell you that i have enabled on departmental email addresses the options forward the messages to the following users/distributions list (mailbox-properties and then mail flow settings-delivery options-Forward to). I have tried to achivie this (block messages to personal email address from outside) via the options of a transport rules either via send a rejection messages to the sender or with the option delete messages. the messages are blocked or deleted but the same happens when an external users sends emails to departmental email address. Below is an example of how the emails from outside are received internally.
i.e.userA@test.com, this user is a member of testgroup
departmental email address :dept@test.com - the option forward to (mailbox-properties and then mail flow settings-delivery options-Forward to) is enabled and the testgroup has been selected.
so when a user from outside sends an email to dept@test.com the messages will be forwarded to all memebers of testgroup 9in our case to userA). - this is correct
Now we want to block emails from outside to personal email address, for that reason i enable the antispam option  Recipient filtering  and i add the userA@test.com . this means that any emails that an outside user sends to this email addressuserA@test.com will be blocked. this is correct. But the same happens when an external user sends an email to departmentaldept@test.com, then the message cannot be received from the userA, because the system blocks all the emails that have as sender an external user and as recipient the userA. the same happens with the transport rule a)reject messages or b) block messages. the system does not understand that the message is sent to departmental email address and the forwarding of the email happens internally due either of the forward To options or via transport rules. Is it any way to achieve this?