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:

  gabriela na bernatova.cz
    SMTP error from remote mail server after end of data:
    host aspmx.l.google.com [142.251.5.27]: 550-5.7.26 This message does not have authentication information or fails to
    550-5.7.26 pass authentication checks. To best protect our users from spam, the
    550-5.7.26 message has been blocked. Please visit
    550-5.7.26  https://support.google.com/mail/answer/81126#authentication for more
    550 5.7.26 information. 199si15327845wma.201 - gsmtp