Here are a few custom functions you can place in Event Espresso's custom_functions.php file to override the default email behavior when sending out registrations for free events that were registered via Multi Event Registration. Please note, this code has only been tested to work in cases where all the events are free. What it will do is concate…

custom_functions.php

<?php
function msec_email_by_session_id($session_id, $send_attendee_email = TRUE, $send_admin_email = TRUE, $multi_reg = FALSE) {
  global $wpdb;
	$sql = "SELECT id FROM " . EVENTS_ATTENDEE_TABLE . " WHERE attendee_session = %s";
	$attendees = $wpdb->get_col( $wpdb->prepare( $sql, $session_id ));
	$admin_email_params = array('email_body'=>'');
	foreach ($attendees as $attendee_id) {
		$data = espresso_prepare_email_data($attendee_id, $multi_reg);
		if ($send_attendee_email == 'true') {
			$attendee_email_params = espresso_prepare_email($data);
			//event_espresso_send_email($attendee_email_params);
		}
		if ($send_admin_email == 'true') {
			$email_params = espresso_prepare_admin_email($data);
			$admin_email_params['send_to'] = $email_params['send_to'];
			$admin_email_params['email_subject'] = $email_params['email_subject'];
			$admin_email_params['email_body'] .= '<----------------------------------------------><br />';
			$admin_email_params['email_body'] .= $email_params['email_subject'] . '<br />';
			$admin_email_params['email_body'] .= '<----------------------------------------------><br />';
			$admin_email_params['email_body'] .= $email_params['email_body'] . '<br />';
			$admin_email_params['headers'] = $email_params['headers'];
		}
	}
	if ($send_admin_email == 'true') {
		event_espresso_send_email($admin_email_params);
	}
	if ($send_attendee_email == 'true') {
		event_espresso_send_email($attendee_email_params);
	}
}

//End msec_email_by_session_id()

if ( ! function_exists('event_espresso_email_confirmations')) {

	function event_espresso_email_confirmations($atts) {
       
		extract($atts);
		//print_r($atts);

		$multi_reg = empty( $multi_reg ) ? FALSE :  $multi_reg;
		$send_admin_email = empty( $send_admin_email ) ? FALSE :  $send_admin_email;
		$send_attendee_email = empty( $send_attendee_email ) ? FALSE :  $send_attendee_email;
		$custom_data = empty( $custom_data ) ? '' :  $custom_data;
		
		if ( ! empty( $attendee_id ) && ! $multi_reg ) { 
		
			email_by_attendee_id($attendee_id, $send_attendee_email, $send_admin_email, $multi_reg, $custom_data);
			
		} elseif ( ! empty( $registration_id ) && ! $multi_reg ) { 
		
			global $wpdb;
            $sql = "SELECT id FROM " . EVENTS_ATTENDEE_TABLE . " WHERE registration_id = %s";
			$attendees = $wpdb->get_col( $wpdb->prepare( $sql, $registration_id ));
			foreach ($attendees as $attendee_id) {
				email_by_attendee_id($attendee_id, $send_attendee_email, $send_admin_email, $multi_reg, $custom_data);
			}
			
		} elseif ( ! empty( $session_id )) { 
		
			msec_email_by_session_id($session_id, $send_attendee_email, $send_admin_email, $multi_reg);
			
		}
	}

}//End event_espresso_email_confirmations()