If you are looking to add any sort of attachment (PDF, large images, etc), we highly recommend uploading that attachment to your website and then creating a unique link to that page. This will not only circumvent any issues in which SPAM filters remove emails with attachments, but will also enable the URL-tracking capabilities included in Core iQ. Your customers/members can then navigate to your website to view and download the secure attachment, and you can track their inbound traffic using Core iQ and Google Analytics.