Forwarding destination for a new account’s catch-all/default address. (Users may modify this value via the Default Address interface in cPanel.) “Fail” rejects the message and notifies the remote SMTP server. This is usually the best choice if you are getting mail attacks. “Blackhole” accepts and processes the message but then silently discards it. This avoids notifying the remote SMTP server but violates SMTP RFC 5321 and generally should not be used.