Updated the code so it delivers proper email:
<?php

This page sends an E-mail to the reporter if an issue is awaiting feedback

require_once( 'core.php' );
$t_core_path = config_get( 'core_path' );
require_once( $t_core_path.'bug_api.php' );
require_once( $t_core_path.'email_api.php' );
$t_subject = 'Issues requiring your attention';
$t_rem_body1 = 'The following issue(s) are awaiting your input';
$t_rem_body2 = 'Please do not reply to this message, use the helpdesk system itself';
//$project=24 ## ERP-Support;
$project=0;
$status=20;
$t_bug_table = config_get( 'mantis_bug_table' );
if ($project>0){
$query = "select id,reporter_id,project_id from $t_bug_table where status=$status and project_id=$project order by reporter_id";
} else{
$query = "select id,reporter_id,project_id from $t_bug_table where status=$status order by reporter_id";
}
$results = mysql_query( $query );
if ($results){
$start = true ;
$list= "";
// first group and store reminder per issue
while ($row1 = mysql_fetch_array($results, MYSQL_NUM)) {
$id = $row1[0];
$handler = $row1[1];
$project = $row1[2];
if ($start){
$handler2 = $handler ;
$start = false ;
}
if ($handler== $handler2){
$list .=" \n\n";
$list .= string_get_bug_view_url_with_fqdn( $id, $handler2 );
} else {
// now send the grouped email
$body = $t_rem_body1. " \n\n";
$body .= $list. " \n\n";
$body .= $t_rem_body2;
$result = email_group_reminder( $handler2, $body);
$handler2 = $handler ;
$list= string_get_bug_view_url_with_fqdn( $id, $handler2 );
}
}
// handle last grouped email
if ($results){
$body = $t_rem_body1. " \n\n";
$body .= $list. " \n\n";
$body .= $t_rem_body2;
$result = email_group_reminder( $handler2, $body);
}
}

Send Grouped reminder

function email_group_reminder( $p_user_id, $issues ) {
$t_username = user_get_field( $p_user_id, 'username' );
$t_email = user_get_email( $p_user_id );
$t_message = $issues ;
$t_subject = 'Issues requiring your attention';
if( !is_blank( $t_email ) ) {
email_send( $t_email, $t_subject, $t_message );
}
}