I can't send mail by "mb_send_mail"

WordPress Questions
1

I’m Japanese.Please excuse my poor English.

The Issue is , I can’t send mail in my contact form.

I use mb_send_email().
This is my code,

$from = 'dev-email@flywheel.local';
$header = '';
$header .= "From: " . $from ." \n";
$header .= "Sender: " . $from ." \n";
$header .= "Reply-To: " . $from . " \n";
$header .= "X-Mailer: PHP/".phpversion();
$opt = '-f '.$from;
mb_language("uni");
mb_internal_encoding("UTF-8");
mb_send_mail($to_mail, $subject, $content, $header,$opt);

Not errors when executed mb_send_mail() .
And, when I check MailHog, the mail log is normally exist in “Inbox”.