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:

  others na gangsto.cz
    SMTP error from remote mail server after RCPT TO:<others na gangsto.cz>:
    host zimbra.gangsto.cz [78.46.142.91]: 550 5.1.1 <others na gangsto.cz>:
    Recipient address rejected: gangsto.cz
  sgsvsag na sawf.cz
    Unrouteable address