MAIL attachments turn to zero kb
Google APP email uses Google designed Encryption.

To set it up you need to use the Google Apps Message Encryption Quick Start Guide.

For the Attachment settings see the Google instructions  Attachment compliance setting

Basically what it means is you have to tell Google APP how to handle the attachments.

To configure Attachment compliance settings for your domain or organizational unit:

Sign in to the Google Admin console.
From the dashboard, go to Apps &gt; Google Apps &gt; Gmail &gt; Advanced settings.
In the Organizations section, highlight your domain or the organizational unit for which you want to configure settings (see Configure advanced settings for Gmail for more details).
Scroll down to the Attachment compliance section:
    If the setting's status is Not configured yet, click Configure (the "Add setting" dialog box displays).
    If the setting's status is Locally applied, click Edit to edit an existing setting (the "Edit setting" dialog box displays), or click Add another to add a new setting (the "Add setting" dialog box displays).
    If the setting’s status is Inherited, click View to view the inherited setting, or click Add another to add a new setting (the "Add setting" dialog box displays).
When you're finished with your changes, click Add setting or Save to close the dialog box.