I'm doing it using PHP. The connection code is the following:

function smtp_mail($to, $from, $subject, $message, $headers = '')
{
   $recipients = explode(',', $to);
   $user = 'mariano.ortega@alvi.com.ar';
   $pass = '------------';
   $smtp_host = 'ssl://smtp.zoho.com';
   $smtp_port = 465;

   if (!($socket = fsockopen($smtp_host, $smtp_port, $errno, $errstr, 15)))
      echo "Could not connect to smtp host '$smtp_host' ($errno) ($errstr)", __FILE__, __LINE__;

   server_parse($socket, '220');

   fwrite($socket, 'EHLO '.'localhost'."\r\n");
   server_parse($socket, '250');

   fwrite($socket, 'AUTH LOGIN'."\r\n");
   server_parse($socket, '334');

   fwrite($socket, base64_encode($user)."\r\n");
   server_parse($socket, '334');

   fwrite($socket, base64_encode($pass)."\r\n");
   server_parse($socket, '235');

   fwrite($socket, 'MAIL FROM: <'.$from.'>'."\r\n");
   server_parse($socket, '250');

   foreach ($recipients as $email)
   {
      fwrite($socket, 'RCPT TO: <'.$email.'>'."\r\n");
      server_parse($socket, '250');
   }

   fwrite($socket, 'DATA'."\r\n");
   server_parse($socket, '354');

   fwrite($socket, 'Subject: '.$subject."\r\n".'To: <'.implode('>, <', $recipients).'>'."\r\n".$headers."\r\n\r\n".$message."\r\n");

   fwrite($socket, '.'."\r\n");
   server_parse($socket, '250');

   fwrite($socket, 'QUIT'."\r\n");
   fclose($socket);

   return true;
}

The "from" is my account as I read on different posts.

The log from the server is the following:

220 mx.zohomail.com SMTP Server ready April 28, 2017 5:10:58 AM 

250-mx.zohomail.com Hello localhost (181.47.250.130 (181.47.250.130))

250-AUTH LOGIN PLAIN

250 SIZE 22020096

334 VXNlcm5hbWU6

334 UGFzc3dvcmQ6

235 Authentication Successful

250 Sender <From: mariano.ortega@alvi.com.ar> OK

250 Recipient <mariano.ortega@alvi.com.ar> OK

354 Ok Send data ending with <CRLF>.<CRLF>

553 Relaying disallowed as <From: mariano.ortega@alvi.com.ar>\

Can you please help?