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:

  hsehserse na sea.cz
    SMTP error from remote mail server after RCPT TO:<hsehserse na sea.cz>:
    host haf.hafici.eu [93.91.157.70]: 550 5.1.1 <hsehserse na sea.cz>:
    Recipient address rejected: User unknown in relay recipient table
  roman.bonek na netron.cz
    SMTP error from remote mail server after end of data:
    host utm.coprosys.cz [77.104.235.178]: 550 Administrative prohibition