Mail delivery failed: returning message to sender

[Mail Delivery System]

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  bh na sde.cz
    SMTP error from remote mail server after RCPT TO:<bh na sde.cz>:
    host mail4.sde.cz [85.93.125.197]: 550 unknown user
  bazzi na yiscali.cz
    Unrouteable address