/etc/msmtprc

defaults
maildomain      example.net
syslog          LOG_MAIL
aliases         /etc/aliases


account         default
host            mail.example.net
port            587
from            srv7@example.net
auth            on
user            user@example.net
password        ********
tls             on
tls_starttls    on
#tls_certcheck   off
tls_fingerprint DB:A0:2A:07:00:F9:E3:23:7D:07:E7:52:3C:95:9D:E6:7E:12:54:3F

Your alias file

# /etc/aliases 
default: me@example.net

A php script to send mail

#!/usr/bin/php
<?php
 
define('TAB',"\t");
 
$user = $_SERVER['LOGNAME'];
$host = exec("hostname -f");
$from = $user.'@'.$host;
 
$to      = 'sweety@example.net';
$subject = 'Testing msmtp';
$message = 'hello from '. $host;
$headers = 'From: '.$from.PHP_EOL;
$headers .= 'X-Mailer: msmtp + PHP '.phpversion();
 
if(mail($to, $subject, $message, $headers))
{
     echo PHP_EOL.TAB.'Your message was successfully accepted for delivery'.PHP_EOL.PHP_EOL;
}else{
     echo PHP_EOL.TAB.'Your message was not accepted for delivery!'.PHP_EOL.PHP_EOL;
}
 
?>