Due to the complex nature of email deliverability, there are scenarios where some people on your mailing lists may not receive the content (drill or practice plan) you sent to them. Deliverability can be affected by user-created filters, spam filtering, corporate firewalls, security policies, etc.
If your emails aren't being delivered, we offer two other sending methods - these options can be accessed by clicking on the "Advanced Options" link below the message field. You will see additional sending methods available. Note that you should only use these options if the primary method is not working.