SSPI authentication attempt from has failed with error .

This error indicates that when a client tried to connect over the POP3 protocol, the authentication attempt with the server failed.

• The POP3 client is configured to use Secure Password Authentication (SPA)

  and the client is in a different domain than the Exchange server.

• There may be a firewall between the client and the server that has SMTP

  command filters configured and the AUTH NTLM command from the Exchange Server

  may be filtered.

• If the POP3 client is in a different domain, configure Outlook Express to

  not use SPA.

• If there is a firewall, ensure that the SMTP Command Filters on the

  firewall do not filter the AUTH NTLM command.

Look for additional error or warning events in the application log.