blocking outgoing attachments ONLY in postfix mail server
 

I have blocked attachments on postfix mail server as below
vi /etc/postfix/main.cf
mime_header_checks = regexp:/etc/postfix/mime_header_checks
in the file
/name=[^>]*\.(jpeg|bmp|tiff|png)/ REJECT.

But postifx blocks even the incoming attachments also. I wanna block only outgoing attachments. Any inputs will be helpful. Thanks in advance.