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:

  emriseq na seznam.cz
    SMTP error from remote mail server after RCPT TO:<emriseq na seznam.cz>:
    host mx1.seznam.cz [77.75.78.42]: 550 5.1.1 Sorry, no mailbox here by that name.
  mamrtinmickanin na seznam.cz
    SMTP error from remote mail server after RCPT TO:<mamrtinmickanin na seznam.cz>:
    host mx1.seznam.cz [77.75.78.42]: 550 5.1.1 Sorry, no mailbox here by that name.
  pida7777 na seznam.cz
    SMTP error from remote mail server after RCPT TO:<pida7777 na seznam.cz>:
    host mx1.seznam.cz [77.75.78.42]: 550 5.1.1 Sorry, no mailbox here by that name.