Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 18407)
+++ wp-includes/formatting.php	(working copy)
@@ -2350,7 +2350,24 @@
 	return apply_filters( 'attribute_escape', $safe_text, $text );
 }
 
+
 /**
+ * Escape an email address
+ *
+ * This works just like esc_html(), except that single quotes are permitted
+ *
+ * @since 3.3
+ *
+ * @param string $email The email address to be escaped
+ * @return string The escaped email
+ */
+function esc_email( $email ) {
+	$safe_email = wp_check_invalid_utf8( $email );
+	$safe_email = _wp_specialchars( $safe_email, ENT_COMPAT );
+	return apply_filters( 'esc_email', $safe_email, $email );
+}
+
+/**
  * Escaping for textarea values.
  *
  * @since 3.1
Index: wp-admin/includes/user.php
===================================================================
--- wp-admin/includes/user.php	(revision 18407)
+++ wp-admin/includes/user.php	(working copy)
@@ -89,7 +89,7 @@
 	}
 
 	if ( isset( $_POST['email'] ))
-		$user->user_email = sanitize_text_field( $_POST['email'] );
+		$user->user_email = sanitize_text_field( stripslashes( $_POST['email'] ) );
 	if ( isset( $_POST['url'] ) ) {
 		if ( empty ( $_POST['url'] ) || $_POST['url'] == 'http://' ) {
 			$user->user_url = '';
Index: wp-admin/user-new.php
===================================================================
--- wp-admin/user-new.php	(revision 18407)
+++ wp-admin/user-new.php	(working copy)
@@ -39,11 +39,12 @@
 	check_admin_referer( 'add-user', '_wpnonce_add-user' );
 
 	$user_details = null;
-	if ( false !== strpos($_REQUEST[ 'email' ], '@') ) {
-		$user_details = get_user_by('email', $_REQUEST[ 'email' ]);
+	$email = stripslashes( $_REQUEST['email'] );
+	if ( false !== strpos( $email, '@' ) ) {
+		$user_details = get_user_by( 'email', $email );
 	} else {
 		if ( is_super_admin() ) {
-			$user_details = get_user_by('login', $_REQUEST[ 'email' ]);
+			$user_details = get_user_by( 'login', $email );
 		} else {
 			wp_redirect( add_query_arg( array('update' => 'enter_email'), 'user-new.php' ) );
 			die();
@@ -59,7 +60,7 @@
 		wp_die(__('Cheatin’ uh?'));
 
 	// Adding an existing user to this blog
-	$new_user_email = esc_html(trim($_REQUEST['email']));
+	$new_user_email = esc_email( trim( $email ) );
 	$redirect = 'user-new.php';
 	$username = $user_details->user_login;
 	$user_id = $user_details->ID;
@@ -102,7 +103,8 @@
 		}
 	} else {
 		// Adding a new user to this blog
-		$user_details = wpmu_validate_user_signup( $_REQUEST[ 'user_login' ], $_REQUEST[ 'email' ] );
+		$email = stripslashes( $_REQUEST[ 'email' ] );
+		$user_details = wpmu_validate_user_signup( $_REQUEST[ 'user_login' ], $email );
 		unset( $user_details[ 'errors' ]->errors[ 'user_email_used' ] );
 		if ( is_wp_error( $user_details[ 'errors' ] ) && !empty( $user_details[ 'errors' ]->errors ) ) {
 			$add_user_errors = $user_details[ 'errors' ];
@@ -111,9 +113,9 @@
 			if ( isset( $_POST[ 'noconfirmation' ] ) && is_super_admin() ) {
 				add_filter( 'wpmu_signup_user_notification', '__return_false' ); // Disable confirmation email
 			}
-			wpmu_signup_user( $new_user_login, $_REQUEST[ 'email' ], array( 'add_to_blog' => $wpdb->blogid, 'new_role' => $_REQUEST[ 'role' ] ) );
+			wpmu_signup_user( $new_user_login, $email, array( 'add_to_blog' => $wpdb->blogid, 'new_role' => $_REQUEST[ 'role' ] ) );
 			if ( isset( $_POST[ 'noconfirmation' ] ) && is_super_admin() ) {
-				$key = $wpdb->get_var( $wpdb->prepare( "SELECT activation_key FROM {$wpdb->signups} WHERE user_login = %s AND user_email = %s", $new_user_login, $_REQUEST[ 'email' ] ) );
+				$key = $wpdb->get_var( $wpdb->prepare( "SELECT activation_key FROM {$wpdb->signups} WHERE user_login = %s AND user_email = %s", $new_user_login, $email ) );
 				wpmu_activate_signup( $key );
 				$redirect = add_query_arg( array('update' => 'addnoconfirmation'), 'user-new.php' );
 			} else {