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:

  fefe na sde.cz
    SMTP error from remote mail server after RCPT TO:<fefe na sde.cz>:
    host mail4.sde.cz [85.93.125.197]: 550 unknown user
  bazant.m na tiscali.cz
    SMTP error from remote mail server after RCPT TO:<bazant.m na tiscali.cz>:
    host tbx.virusfree.cz [5.180.49.36]: 550 user not exist
  deathman na centrum.cz
    SMTP error from remote mail server after RCPT TO:<deathman na centrum.cz>:
    host cax.virusfree.cz [5.180.49.35]: 554 5.7.1 <deathman na centrum.cz>:
    Recipient address rejected: Access denied, user does not exist