Microsoft Security Bulletin MS06-019 - Be careful
So, before you apply Microsoft Security Bulletin MS06-019 on Exchange Servers - Be careful. Take a look at the known issues.
912918 (http://support.microsoft.com/kb/912918/) Users cannot send e-mail messages from a mobile device or from a shared mailbox in Exchange 2000 Server and in Exchange Server 2003.
First, Find accounts that have the Full Mailbox Access permission without the Send As permission using the script from http://support.microsoft.com/kb/912918/ and grant the Send As permission either manually using DSA.msc or using the script -SetAll switch.
And then, you are ready to apply MS06-019.