Just noticed today that Microsoft has release update rollup 5 for Exchange 2010 SP1.
It contains the Exchange 2010 change called out in KB Article 2543879: PDF attachment from a Mac Mail client is not displayed when you use Outlook 2010 to open the email message in an Exchange Server 2007 SP3 environment.
I have seen this problem more and more lately.We can’t see the PDF file as an attachment at all in Outlook but can see the attachment fine on our mobile devices.
Go to http://blogs.technet.com/b/exchange/archive/2011/08/23/released-update-rollup-5-for-exchange-2010-sp1.aspx to get more information.