The sender is blank in the Track and Trace logs/results or doesn't match when the email is received.
Track and Trace logs show the Env Sender, not the Body Sender. Some company's or individuals designate their emails to go out as such. This situation most commonly occurs for emails sent from distribution services.
Most often, mail clients will provide the Body Sender information as the sending address. For distribution lists in particular, the Env Sender can be lengthy and can confuse or alarm the recipient. In addition, it will most likely be dismissed as spam.