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:

  -errors na ashk.cz
    SMTP error from remote mail server after RCPT TO:<-errors na ashk.cz>:
    host mail.ashk.cz [77.236.222.45]: 550 5.7.0 Your server IP address is in the SpamCop database, bye