If your client clicks the link the "unsubscribe" link at the bottom of an email sent from Matrix, it will disable their auto email search.
Follow the steps below to re-enable your clients auto email:
1. Your client must send a blank email to firstname.lastname@example.org from the email address they used when they unsubscribed. Please Note: They do not have to fill in a subject line or type a message
2. Go to the My Matrix tab, and click on Auto Emails.
3. Click either the name of the Auto Email or the arrow button , then click Settings.
4. At the bottom of your Auto Email's settings page, change it back to Enabled, then click Save.
Your client should now be able to receive emails from Matrix.