If you take a look at the Exchange Admin console in Office 365 and then setup a new mobile device policy you may find that some of the more advanced options, such as block attachments, is not available in the admin console:
You may notice the following message in the mobile device policy when you select any of the polices that have been setup:
This basically means that to configure some of the controls you will need to use PowerShell in order to make changes. Two steps can achieve this:
1. Connect to Exchange Online via PowerShell (http://technet.microsoft.com/en-us/library/jj984289(v=exchg.150).aspx)
2. Use the Set-ActiveSyncMailboxPolicy command to enable or disable the settings that you wish (http://technet.microsoft.com/en-us/library/bb123756(v=exchg.150).aspx)
If you take a look at the URL above for the Set- ActiveSyncMailboxPolicy command, under parameters will give you a full list of the policies that you can apply to the mobile devices.