We have new features on our Vtiger integration apps with the mass mailer programs — Mailchimp and Constant Contact.  Those are the two biggest players in the market so that is where we have focused our efforts.

We now sync the clicks, bounces and opens to fields on the vtiger contact record from the mailer program.  This way you can create filters and workflows to have employees:

• follow up right away with your readers that are clicking on your email.  We have an optional feature to auto-schedule an activity for follow up immediately upon sync of a click.
• know who is opening your emails and decide if you want to do some targeted follow up
• clean up the bounces.  Some of your bounces will be clients that have new email addresses, etc.

Here is a link to the Vtiger Constant Contact integration page.

Here is a link to the Vtiger Mailchimp integration page