When you view the Failures Report you may notice that Type field is displayed as Permanent, Temporary, or Suppressed. When you download the report you will see that the Type field is specified as 0, 1, or 2. Here is the translation:
If you are attempting to keep your list clean, you should remove any permanent or suppressed addresses from your list. By removing these addresses you will cut down on the suppressed failures and reduce the overall number of messages you are sending through the SMTP server.
0 – Temporary failure. The message failed to be delivered, but was not suppressed for future delivery attempts.
1 – Permanent failure. The message failed to be delivered, but is now suppressed for future delivery attempts.
2 – Suppressed. The message was previously suppressed, and delivery was not attempted at all.