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:

  cx na xvx.cz
    SMTP error from remote mail server after RCPT TO:<cx na xvx.cz>:
    host aspmx.l.google.com [74.125.133.27]: 550-5.1.1 The email account that you tried to reach does not exist. Please try
    550-5.1.1 double-checking the recipient's email address for typos or
    550-5.1.1 unnecessary spaces. Learn more at
    550 5.1.1  https://support.google.com/mail/?p=NoSuchUser k22si7289552wmj.64 - gsmtp
  milkar na stasis.cz
    SMTP error from remote mail server after RCPT TO:<milkar na stasis.cz>:
    host mx10.onebit.cz [178.238.37.193]: 550 5.1.1 <milkar na stasis.cz>:
    Recipient address rejected: User unknown in virtual mailbox table