diff --git a/includes/lib/general.php b/includes/lib/general.php
index 127c6b7..e7e54db 100644
--- a/includes/lib/general.php
+++ b/includes/lib/general.php
@@ -1,6 +1,6 @@
 <? /*
     LibreSSL - CAcert web application
-    Copyright (C) 2004-2011  CAcert Inc.
+    Copyright (C) CAcert Inc.
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -16,32 +16,91 @@
     Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
+/**
+ * Walk through the email address environment variables that Apache httpd
+ * might have set and put them into an array.
+ *
+ * The function ensures that unique addresses are returned.
+ *
+ * @return array
+ */
+function get_email_addresses_from_client_cert() {
+	$addresses = array();
+	$maxAddresses = 10; // implement a hard boundary to avoid endless loop
+
+	// try SAN email addresses first
+	$envNameBase = "SSL_CLIENT_SAN_Email";
+	for ($i = 0; $i <= $maxAddresses; $i++) {
+		$envName = sprintf("%s_%d", $envNameBase, $i);
+		if (!array_key_exists($envName, $_SERVER)) {
+			break;
+		}
+		$addresses[] = $_SERVER[$envName];
+	}
+
+	if (count($addresses) > 0) {
+		return array_unique($addresses);
+	}
+
+	// fallback for older Apache httpd versions that do not support email SAN fields
+	$envNameBase = "SSL_CLIENT_S_DN_Email";
+
+	if (array_key_exists($envNameBase, $_SERVER)) {
+		$addresses[] = $_SERVER[$envNameBase];
+	}
+
+	for ($i = 1; $i <= $maxAddresses; $i++) {
+		$envName = sprintf("%s_%d", $envNameBase, $i);
+		if (array_key_exists($envName, $_SERVER)) {
+			$addresses[] = $_SERVER[$envName];
+		}
+	}
+
+	return array_unique($addresses);
+}
+
 /**
  * Checks if the user may log in and retrieve the user id
  *
  * Usually called with $_SERVER['SSL_CLIENT_M_SERIAL'] and
- * 	$_SERVER['SSL_CLIENT_I_DN_CN']
+ *    $_SERVER['SSL_CLIENT_I_DN_CN']
  *
  * @param $serial string
- * 	usually $_SERVER['SSL_CLIENT_M_SERIAL']
+ *    usually $_SERVER['SSL_CLIENT_M_SERIAL']
  * @param $issuer_cn string
- * 	usually $_SERVER['SSL_CLIENT_I_DN_CN']
+ *    usually $_SERVER['SSL_CLIENT_I_DN_CN']
+ * @param $addresses array
+ *  list of email addresses from the certificate
  * @return int
- * 	the user id, -1 in case of error
+ *    the user id, -1 in case of error
+ *
+ * @see get_email_addresses_from_client_cert()
  */
-function get_user_id_from_cert($serial, $issuer_cn)
-{
-	$query = "select `memid` from `emailcerts` where
-			`serial`='".mysql_escape_string($serial)."' and
-			`rootcert`= (select `id` from `root_certs` where
-				`Cert_Text`='".mysql_escape_string($issuer_cn)."') and
-			`revoked`=0 and disablelogin=0 and
-			UNIX_TIMESTAMP(`expire`) - UNIX_TIMESTAMP() > 0";
+function get_user_id_from_cert($serial, $issuer_cn, $addresses) {
+	$addresses_for_sql = array_map('mysql_real_escape_string', $addresses);
+
+	$query = sprintf("SELECT DISTINCT ec.`memid`
+FROM `emailcerts` ec
+         JOIN root_certs r ON r.id = ec.rootcert
+         JOIN email e ON ec.memid = e.memid
+WHERE ec.serial = '%s'
+  AND r.`Cert_Text` = '%s'
+  AND e.email IN ('%s')
+  AND ec.revoked = 0
+  AND ec.disablelogin = 0
+  AND UNIX_TIMESTAMP(ec.expire) > UNIX_TIMESTAMP()", mysql_real_escape_string($serial),
+		mysql_real_escape_string($issuer_cn), implode("', '", $addresses_for_sql));
+
 	$res = mysql_query($query);
-	if(mysql_num_rows($res) > 0)
-	{
-		$row = mysql_fetch_assoc($res);
-		return intval($row['memid']);
+	if ($res === false) {
+		trigger_error(sprintf("MySQL error %d: %s", mysql_errno(), mysql_error()));
+
+		return -1;
+	}
+
+	if (mysql_num_rows($res) === 1) {
+		$row = mysql_fetch_row($res);
+		return intval($row[0]);
 	}
 
 	return -1;
diff --git a/includes/loggedin.php b/includes/loggedin.php
index c14f8c2..30c6b55 100644
--- a/includes/loggedin.php
+++ b/includes/loggedin.php
@@ -54,7 +54,7 @@
 	if($_SERVER['HTTP_HOST'] == $_SESSION['_config']['securehostname'] && ($_SESSION['profile']['id'] == 0 || $_SESSION['profile']['loggedin'] == 0))
 	{
 		$user_id = get_user_id_from_cert($_SERVER['SSL_CLIENT_M_SERIAL'],
-				$_SERVER['SSL_CLIENT_I_DN_CN']);
+				$_SERVER['SSL_CLIENT_I_DN_CN'], get_email_addresses_from_client_cert());
 
 		if($user_id >= 0)
 		{
diff --git a/www/index.php b/www/index.php
index 8c5560c..fed651b 100644
--- a/www/index.php
+++ b/www/index.php
@@ -153,7 +153,7 @@ require_once('../includes/notary.inc.php');
 	{
 		include_once("../includes/lib/general.php");
 		$user_id = get_user_id_from_cert($_SERVER['SSL_CLIENT_M_SERIAL'],
-				$_SERVER['SSL_CLIENT_I_DN_CN']);
+				$_SERVER['SSL_CLIENT_I_DN_CN'], get_email_addresses_from_client_cert());
 
 		if($user_id >= 0)
 		{