Message was not sent.Mailer error: Language string failed to load: recipients_failed

I have created a script to work between two programs we have. The first creates an e-mail with phone numbers followed by the txt message, in the body.

the script i have written then reads the mailbox the emails are sent to and extracts the data. The txts are then sent to our txt server again by e-mail.

The format of the email must be,
To field: phonenumber@send.sms
body: txt message.

my script creats this layout without problems. The error comes from the script to send the txt by email (please see the code below).

if i send a message to support@nwmservices.co.uk from the script, it's fine. As soon as i change it to phonenumber@send.sms it gives the following error.

Message was not sent.Mailer error: Language string failed to load: recipients_failed.

i have also tried it with a name just incase it didn't like the phone number, but i still get,

Message was not sent.Mailer error: Language string failed to load: recipients_failedSupport@send.sms

send.sms uses a conector within exchnage as send.sms is not a valid domain on the internet.

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$mail = new PHPMailer();
$mail->IsSMTP(); // telling the class to use SMTP
$mail->Host = "192.168.16.2"; // SMTP server
$mail->From = "matt@cowleyit.co.uk";
$mail->AddAddress("$to");
 
$mail->Subject = "Autoskills txt";
$mail->Body = $body;
 
 
if(!$mail->Send())
{
   echo 'Message was not sent.';
   echo 'Mailer error: ' . $mail->ErrorInfo;
}
else
{
   echo 'Message has been sent.';
}