diff --git a/phpBB/includes/functions_privmsgs.php b/phpBB/includes/functions_privmsgs.php
index 447920cfd5..d2fce000aa 100644
--- a/phpBB/includes/functions_privmsgs.php
+++ b/phpBB/includes/functions_privmsgs.php
@@ -1083,6 +1083,166 @@ function delete_pm($user_id, $msg_ids, $folder_id)
 	return true;
 }
 
+/**
+* Delete all PM(s) for a given user and delete the ones without references
+*
+* @param	int		$user_id	ID of the user whose private messages we want to delete
+*
+* @return	boolean		False if there were no pms found, true otherwise.
+*/
+function phpbb_delete_user_pms($user_id)
+{
+	global $db, $user, $phpbb_root_path, $phpEx;
+
+	$user_id = (int) $user_id;
+
+	if (!$user_id)
+	{
+		return false;
+	}
+
+	// Get PM Information for later deleting
+	// The two queries where split, so we can use our indexes
+	// Part 1: get PMs the user received
+	$sql = 'SELECT msg_id, author_id, folder_id, pm_unread, pm_new
+		FROM ' . PRIVMSGS_TO_TABLE . '
+		WHERE user_id = ' . $user_id;
+	$result = $db->sql_query($sql);
+
+	$undelivered_msg = $undelivered_user = $delete_ids = array();
+	while ($row = $db->sql_fetchrow($result))
+	{
+		if ($row['author_id'] == $user_id && $row['folder_id'] == PRIVMSGS_NO_BOX)
+		{
+			// Undelivered messages
+			$undelivered_msg[] = $row['msg_id'];
+
+			if (isset($undelivered_user[$row['user_id']]))
+			{
+				++$undelivered_user[$row['user_id']];
+			}
+			else
+			{
+				$undelivered_user[$row['user_id']] = 1;
+			}
+		}
+
+		$delete_ids[(int) $row['msg_id']] = (int) $row['msg_id'];
+	}
+	$db->sql_freeresult($result);
+
+	// Part 2: get PMs the user sent
+	$sql = 'SELECT msg_id, author_id, folder_id, pm_unread, pm_new
+		FROM ' . PRIVMSGS_TO_TABLE . '
+		WHERE author_id = ' . $user_id . '
+				AND folder_id = ' . PRIVMSGS_NO_BOX;
+	$result = $db->sql_query($sql);
+
+	while ($row = $db->sql_fetchrow($result))
+	{
+		if ($row['author_id'] == $user_id && $row['folder_id'] == PRIVMSGS_NO_BOX)
+		{
+			// Undelivered messages
+			$undelivered_msg[] = $row['msg_id'];
+
+			if (isset($undelivered_user[$row['user_id']]))
+			{
+				++$undelivered_user[$row['user_id']];
+			}
+			else
+			{
+				$undelivered_user[$row['user_id']] = 1;
+			}
+		}
+
+		$delete_ids[(int) $row['msg_id']] = (int) $row['msg_id'];
+	}
+	$db->sql_freeresult($result);
+
+	if (empty($delete_ids))
+	{
+		return false;
+	}
+
+	$db->sql_transaction('begin');
+
+	if (sizeof($undelivered_msg))
+	{
+		$sql = 'DELETE FROM ' . PRIVMSGS_TABLE . '
+			WHERE ' . $db->sql_in_set('msg_id', $undelivered_msg);
+		$db->sql_query($sql);
+	}
+
+	// Reset the userīs pm count to 0
+	if (isset($undelivered_user[$user_id]))
+	{
+		$sql = 'UPDATE ' . USERS_TABLE . '
+			SET user_new_privmsg = 0,
+				user_unread_privmsg = 0
+			WHERE user_id = ' . $user_id;
+		$db->sql_query($sql);
+		unset($undelivered_user[$user_id]);
+	}
+
+	foreach ($undelivered_user as $_user_id => $count)
+	{
+		$sql = 'UPDATE ' . USERS_TABLE . '
+			SET user_new_privmsg = user_new_privmsg - ' . $count . ',
+				user_unread_privmsg = user_unread_privmsg - ' . $count . '
+			WHERE user_id = ' . $_user_id;
+		$db->sql_query($sql);
+	}
+
+	// Delete private message data
+	$sql = 'DELETE FROM ' . PRIVMSGS_TO_TABLE . "
+		WHERE user_id = $user_id
+			AND " . $db->sql_in_set('msg_id', $delete_ids);
+	$db->sql_query($sql);
+
+	// Now we have to check which messages we can delete completely
+	$sql = 'SELECT msg_id
+		FROM ' . PRIVMSGS_TO_TABLE . '
+		WHERE ' . $db->sql_in_set('msg_id', $delete_ids);
+	$result = $db->sql_query($sql);
+
+	while ($row = $db->sql_fetchrow($result))
+	{
+		unset($delete_ids[$row['msg_id']]);
+	}
+	$db->sql_freeresult($result);
+
+	if (!empty($delete_ids))
+	{
+		// Check if there are any attachments we need to remove
+		if (!function_exists('delete_attachments'))
+		{
+			include($phpbb_root_path . 'includes/functions_admin.' . $phpEx);
+		}
+
+		delete_attachments('message', $delete_ids, false);
+
+		$sql = 'DELETE FROM ' . PRIVMSGS_TABLE . '
+			WHERE ' . $db->sql_in_set('msg_id', $delete_ids);
+		$db->sql_query($sql);
+	}
+
+	// Set the remaining author id to anonymous
+	// This way users are still able to read messages from users being removed
+	$sql = 'UPDATE ' . PRIVMSGS_TO_TABLE . '
+		SET author_id = ' . ANONYMOUS . '
+		WHERE author_id = ' . $user_id;
+	$db->sql_query($sql);
+
+	$sql = 'UPDATE ' . PRIVMSGS_TABLE . '
+		SET author_id = ' . ANONYMOUS . '
+		WHERE author_id = ' . $user_id;
+	$db->sql_query($sql);
+
+	$db->sql_transaction('commit');
+
+	return true;
+}
+
 /**
 * Rebuild message header
 */
diff --git a/phpBB/includes/functions_user.php b/phpBB/includes/functions_user.php
index 83316be2a3..5a6a0b4a05 100644
--- a/phpBB/includes/functions_user.php
+++ b/phpBB/includes/functions_user.php
@@ -528,62 +528,12 @@ function user_delete($mode, $user_id, $post_username = false)
 		WHERE session_user_id = ' . $user_id;
 	$db->sql_query($sql);
 
-	// Remove any undelivered mails...
-	$sql = 'SELECT msg_id, user_id
-		FROM ' . PRIVMSGS_TO_TABLE . '
-		WHERE author_id = ' . $user_id . '
-			AND folder_id = ' . PRIVMSGS_NO_BOX;
-	$result = $db->sql_query($sql);
-
-	$undelivered_msg = $undelivered_user = array();
-	while ($row = $db->sql_fetchrow($result))
+	// Clean the private messages tables from the user
+	if (!function_exists('phpbb_delete_user_pms'))
 	{
-		$undelivered_msg[] = $row['msg_id'];
-		$undelivered_user[$row['user_id']][] = true;
-	}
-	$db->sql_freeresult($result);
-
-	if (sizeof($undelivered_msg))
-	{
-		$sql = 'DELETE FROM ' . PRIVMSGS_TABLE . '
-			WHERE ' . $db->sql_in_set('msg_id', $undelivered_msg);
-		$db->sql_query($sql);
-	}
-
-	$sql = 'DELETE FROM ' . PRIVMSGS_TO_TABLE . '
-		WHERE author_id = ' . $user_id . '
-			AND folder_id = ' . PRIVMSGS_NO_BOX;
-	$db->sql_query($sql);
-
-	// Delete all to-information
-	$sql = 'DELETE FROM ' . PRIVMSGS_TO_TABLE . '
-		WHERE user_id = ' . $user_id;
-	$db->sql_query($sql);
-
-	// Set the remaining author id to anonymous - this way users are still able to read messages from users being removed
-	$sql = 'UPDATE ' . PRIVMSGS_TO_TABLE . '
-		SET author_id = ' . ANONYMOUS . '
-		WHERE author_id = ' . $user_id;
-	$db->sql_query($sql);
-
-	$sql = 'UPDATE ' . PRIVMSGS_TABLE . '
-		SET author_id = ' . ANONYMOUS . '
-		WHERE author_id = ' . $user_id;
-	$db->sql_query($sql);
-
-	foreach ($undelivered_user as $_user_id => $ary)
-	{
-		if ($_user_id == $user_id)
-		{
-			continue;
-		}
-
-		$sql = 'UPDATE ' . USERS_TABLE . '
-			SET user_new_privmsg = user_new_privmsg - ' . sizeof($ary) . ',
-				user_unread_privmsg = user_unread_privmsg - ' . sizeof($ary) . '
-			WHERE user_id = ' . $_user_id;
-		$db->sql_query($sql);
+		include($phpbb_root_path . 'includes/functions_privmsgs.' . $phpEx);
 	}
+	phpbb_delete_user_pms($user_id);
 
 	$db->sql_transaction('commit');
 
diff --git a/phpBB/install/database_update.php b/phpBB/install/database_update.php
index 6097341ace..c700b483a5 100644
--- a/phpBB/install/database_update.php
+++ b/phpBB/install/database_update.php
@@ -2026,7 +2026,7 @@ function change_database_data(&$no_updates, $version)
 		// No changes from 3.0.10-RC3 to 3.0.10
 		case '3.0.10-RC3':
 		break;
-		
+
 		// Changes from 3.0.10 to 3.0.11-RC1
 		case '3.0.10':
 			// Updates users having current style a deactivated one
@@ -2050,6 +2050,44 @@ function change_database_data(&$no_updates, $version)
 				_sql($sql, $errored, $error_ary);
 			}
 
+			// Delete orphan private messages
+			$batch_size = 500;
+
+			$sql_array = array(
+				'SELECT'	=> 'p.msg_id',
+				'FROM'		=> array(
+					PRIVMSGS_TABLE	=> 'p',
+				),
+				'LEFT_JOIN'	=> array(
+					array(
+						'FROM'	=> array(PRIVMSGS_TO_TABLE => 't'),
+						'ON'	=> 'p.msg_id = t.msg_id',
+					),
+				),
+				'WHERE'		=> 't.user_id IS NULL',
+			);
+			$sql = $db->sql_build_query('SELECT', $sql_array);
+
+			do
+			{
+				$result = $db->sql_query_limit($sql, $batch_size);
+
+				$delete_pms = array();
+				while ($row = $db->sql_fetchrow($result))
+				{
+					$delete_pms[] = (int) $row['msg_id'];
+				}
+				$db->sql_freeresult($result);
+
+				if (!empty($delete_pms))
+				{
+					$sql = 'DELETE FROM ' . PRIVMSGS_TABLE . '
+						WHERE ' . $db->sql_in_set('msg_id', $delete_pms);
+					_sql($sql, $errored, $error_ary);
+				}
+			}
+			while (sizeof($delete_pms) == $batch_size);
+
 			$no_updates = false;
 		break;
 	}