This is not a Lesson feature, nor is it something found in the course settings. While an excellent post, it does not belong here
We use the contributed code "Certificate" for this purpose. The 1.9 version will send emails to multiple addresses and has several choices for conditions. Earlier versions will send email to a single email address and conditions will be less robust. Certificate in any version is stable and should be included in 2.0 ! Enough said.
Hope this helps. Chris