I can't receive emails Ubuntu 18.04 with Postfix (PHP 7.2-FPM, NGINX)

Hello everyone, I spend whole night trying to get it work and I no success… I don’t know whats wrong and asking you for help.

What I want to do is make php mail() form to work, but I’m not receiving mail() function submitted.

PHP Settings

sendmail_path = /usr/sbin/sendmail -t -i

PHP Mail Script:

   <?php
        ini_set( 'display_errors', 1 );
        error_reporting( E_ALL );
        $from = "arnas@mydomain.com";
        $to = "arnas@mydomain.com";
        $subject = "Testing email #1";
        $message = "Test message";
        $headers = "From:" . $from;
        mail($to,$subject,$message, $headers);
        echo "Test email sent";
    ?>

Postfix installation:

sudo apt-get update
sudo apt install -y mailutils

Select Internet Site and press ENTER. System mail name: mydomain.com

sudo nano /etc/postfix/main.cf

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = mydomain.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = mydomain.com, mydomain.com, localhost.localdomain, localhost
relayhost = 
mynetworks = 127.0.0.0/8
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = ipv4

After all configuration I have tried to send test email also from command line as follows:

echo "Test Email message body" | mail -s "Email test subject" name@mydomain.com

After that I viewed log sudo tail /var/log/mail.log and it prints:

Jan 21 09:23:42 DROPLET-LEMP-NEW postfix/pickup[16088]: EFD2FFF3A7: uid=0 from=<root@DROPLET-LEMP-NEW>
Jan 21 09:23:42 DROPLET-LEMP-NEW postfix/cleanup[16126]: EFD2FFF3A7: message-id=<20200121092342.EFD2FFF3A7@mydomain.com>
Jan 21 09:23:42 DROPLET-LEMP-NEW postfix/qmgr[16089]: EFD2FFF3A7: from=<root@DROPLET-LEMP-NEW>, size=346, nrcpt=1 (queue active)
Jan 21 09:23:43 DROPLET-LEMP-NEW postfix/local[16128]: EFD2FFF3A7: to=<arnas@mydomain.com>, relay=local, delay=0.04, delays=0.02/0.01/0/0.01, dsn=5.1.1, status=bounced (unknown user: "arnas")
Jan 21 09:23:43 DROPLET-LEMP-NEW postfix/cleanup[16126]: 024D7FF3A8: message-id=<20200121092343.024D7FF3A8@mydomain.com>
Jan 21 09:23:43 DROPLET-LEMP-NEW postfix/qmgr[16089]: 024D7FF3A8: from=<>, size=2117, nrcpt=1 (queue active)
Jan 21 09:23:43 DROPLET-LEMP-NEW postfix/bounce[16129]: EFD2FFF3A7: sender non-delivery notification: 024D7FF3A8
Jan 21 09:23:43 DROPLET-LEMP-NEW postfix/qmgr[16089]: EFD2FFF3A7: removed
Jan 21 09:23:43 DROPLET-LEMP-NEW postfix/smtp[16131]: 024D7FF3A8: to=<root@DROPLET-LEMP-NEW>, relay=none, delay=0.02, delays=0/0.01/0.01/0, dsn=5.4.6, status=bounced (mail for DROPLET-LEMP-NEW loops back to myself)
Jan 21 09:23:43 DROPLET-LEMP-NEW postfix/qmgr[16089]: 024D7FF3A8: removed

I have no clue whats going on here :(