----- The following addresses had permanent fatal errors -----
    (reason: 505 5.7.3 Client was not authenticated)
    ----- Transcript of session follows -----
... while talking to class6c.com.:
>>> MAIL From:<kjn at interphos.com> SIZE=2435
<<< 505 5.7.3 Client was not authenticated
554 5.0.0 <>... Service unavailable