After configuring the Invite Users to Create/Update Q&A Profiles user enforcement rule, the users do not receive an email.
Confirm the SMTP setting are correct by opening the Admin site and clicking General Settings | SMTP Servers
Test to see if emails can be sent from Password Manager:
The email sent to invite users to create/update their Q&A profiles is sent out on a scheduled basis using the Invitation to Create/Update Q&A Profiles task. Confirm this scheduled task has been enabled by selecting General Settings | Scheduled Tasks.