“Undisclosed Recipients”

When we receive an email, we usually look at the Sender field to see who it is from. Even that does not guarantee the sender is who they claim to be, but if the Sender field is blank, or if the To field shows “undisclosed recipients”, be extra cautious.

The obvious implication is that the real sender is trying to hide their identity. They also might be using the blind carbon copy (BCC) field to hide recipients, so it is not apparent that the email is going to thousands or millions of people.