Hi Chelsey,
The "Request Accepted. Beginning processing." message is for something else (to know that the email as a whole was accepted and started being processed). What you want to do is open the contact/lead record that was blocked. Then go to the Email Events associated to that person and find the previous "Invalid Recipient" or "DNS Failure" event, or 4 "Soft Bounce" events. Those events are the ones that will have the messages about the bounce on them. This person is an Excluded Email because they previously bounced before you even tried to send the email that they were excluded on. That is why you want to look at previous Email Event records.
Thanks for using the forum!