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:

  sevcikova na ham.cz
    SMTP error from remote mail server after RCPT TO:<sevcikova na ham.cz>:
    host mx.ham.cz [90.181.190.107]: 550 5.7.1 Service unavailable; client [62.36.20.208] blocked using bl.mailspike.net