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:

  prospam2 na o2active.cz
    SMTP error from remote mail server after RCPT TO:<prospam2 na o2active.cz>:
    host smtp-in.quick.cz [90.176.151.97]: 554 5.7.1 Service unavailable; Client host [62.36.20.208] blocked using bl.iol.cz
  pospisil na gncz.cz
    SMTP error from remote mail server after RCPT TO:<pospisil na gncz.cz>:
    host mail.dc3.cz [81.0.217.5]: 550 Recipient not found