If you open the Queue Viewer tool from the Toolbox node on the Exchange Management Console, the Last Error field displays an error message that resembles the following:Ĥ51 4.4.0 Primary target IP address responded with: '454 4.7.0 Temporary authentication failure.' Attempted failover to alternate host, but that did not succeed. In an Exchange server environment, some e-mail messages are stuck in a remote delivery queue that should have been transferred to another internal Exchange server in the Exchange organization.