sendmail: fatal: /etc/mailname: cannot open file: Permission denied

Hi everyone,
I have (ISPconf3 w.3 clients 6+webpages, @server, Apache2 w. php 7.4 - when I execute "php mail.php" in cmd line, Message is sent successfully.
---------------------------
$to = 'tk@....';
$subject = 'Marriage Proposal';
$message = 'Hi Jane, will you marry me?';
$from = 'peterparker@...';

// Sending email
if(mail($to, $subject, $message, $headers)){
echo 'Your mail has been sent successfully.';
} else{
echo 'Unable to send email. Please try again5 .';
}
?>
-------------------------------
(Booth @ existing).

if I open the same .php from the browser, I will see error message from the script "Unable to send email. Please try again5 ."

I find in Apache2.log error: sendmail: fatal: /etc/mailname: cannot open file: Permission denied
I tried to change owner of mailname to sendmail:sendmail / sendmail:root w/o any change.

- I believe that from same problem does not work Autoresponder in ISPconfig.

Any suggestions how to resolve it ?

 

I feel so lame It was 640 and +4 fixed phpmail & also autoresponder issue. Thank you Jesse.