The timeline error message "The (SmartPlan Name) SmartPlan could not deliver an email to (contact name) because Command Mail has blocklisted (email address)" on your contact's timeline means is that the email is not able to be sent to this contact at that email address.
There are a few reasons for this message, including:
- User has clicked on unsubscribe and therefore the agent cannot send email from that Smartplan.
- User has marked Smartplan mailer email address as spam enough times that the email provider has blocked it.
- Email address is invalid or doesn't exist.