Icons in email notifications are shown as file attachments in Mail.app

When using OSX Mail.app I see attachments in the footer. I assume these are for the images in the content.

The problem is with how the MIME container for the email is constructed. It's possible to construct it in such a way that inline images don't display as attachments. Confluence emails currently do this, I suggest comparing the source of confluence emails with a JIRA email to see the difference in how the images are included.