MX list error

[Alessandro Coppelli <coppelli_(_at_)_dsea_(_dot_)_unipi_(_dot_)_it>]

 ----- The following addresses had permanent fatal errors -----
<pallottino_(_at_)_piaggio_(_dot_)_ccii_(_dot_)_unipi_(_dot_)_it>

   ----- Transcript of session follows -----
554 5.0.0 MX list for piaggio.ccii.unipi.it. points back to
euclid.piaggio.ccii.unipi.it
554 5.3.5 <pallottino_(_at_)_piaggio_(_dot_)_ccii_(_dot_)_unipi_(_dot_)_it>... Local configuration
error


  What does it mean this error ?

        Alessandro