User is not receiving an email, but the Track and Trace shows Delivered to recipient network, e.g.
In the Delivery section, you also see Delivered to recipient network, but the user didn't receive this email.
Email Security.cloud
The message was delivered to the recipient's mailserver. It can be tracked by the mailserver administrator, with the Message ID visible in Track and Trace.
You can contact Technical Support if you need delivery logs for the message.