Ensuring Email Deliverability
Many email providers will block email with return addresses which do not match the domain they are sent from. So to ensure that email sent from Concrete CMS arrive at the intended recipient, be sure to set the System Email Addresses in the System & Settings > Email section of the Dashboard.
Another setting to be aware of is the domain's SPF and DKIM records. These should also be set correctly at the DNS record level to help validate that emails sent from a domain really came from that domain.