It means the email was diverted: the platform has a redirect address configured (an internal System Email - Redirect To value, or a server-level test redirect used on staging sites), so instead of going to the customer the message was delivered to that address with (TO:customer@address) added to the subject. The To column still shows the intended customer, while Redirected To shows where it really went. BCC copies are not sent while a redirect is active. This redirect is not exposed in the Client Config screens you can edit - if you see it on your live site unexpectedly, ask Sprwt support to clear it.