I check the mail queue and the logs and this time I found some strange thing. I used command "grep -r "emailemailemail.com" /var/log/mail.log" and result is in attached .txt file. If I understand properly there is many tries to send from [hidden email] to [hidden email] but nothing happens later because of failing connection to emailemailemail.com on port 25.
Thank you Tom for answer. For me is quite strange, because [hidden email] is my mailbox. I didn't send any email to [hidden email]. Btw, how do you know that receiving server does not exists - due to failing connection on 25 port?