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. There are two steps to re-enable their auto email:
Your client must send a blank email to email@example.com from the email address they used when they unsubscribed.
**They do not have to fill in a subject line or type a message.**
You must go to My Matrix, choose "Auto Emails". Click on the name of the auto email (under Subject column) or the corresponding downward-pointing arrow to open the full options; then click "Settings".
On the settings screen, under your message, change the auto email to "Enabled" and click save.
Your client should now be able to receive emails from Matrix.