The Zip compress attachments feature will compress attachments en-route to reduce the file size of the attachments which the recipient receives in their inbox.  This service is not compatible with encryption due to an Adobe Reader security setting.

1. Compose an email and attach the documents.
2. Click on the Send Registered button to open the features panel.
3. On the Attachments section check the Zip Compress option box

4. Click on the Send button

 Note: The attachments in the “Sent Items” folder are not Zip compressed.