Please add following condition.
$mailSent = get_user_meta($us_id, 'mail_sent', true);
if($mailSent){
update_user_meta($us_id, 'mail_sent', 'mail sent');
}else{
$borrower_mail=wp_mail($to, $subject, $body);
}
Please add following condition.
$mailSent = get_user_meta($us_id, 'mail_sent', true);
if($mailSent){
update_user_meta($us_id, 'mail_sent', 'mail sent');
}else{
$borrower_mail=wp_mail($to, $subject, $body);
}