Sendmail or GnuPG or Mutt problem how to know ?

[Pac]

Hi,

every time I try to sign a message with GnuPG under Mutt I receive
after a few second this error message :

sendmail: 451 See http://pobox.com/~djb/docs/smtplf.html


what is it and how to fix this ?


thanks
Best Regards
-- 
R.Pac