This should be 'crypt-md5'.
This is a harmless existence-check error.

Dear all,

Thank you for providing the great horde app. However, the password 
tool does not seem to work. I have stored my passwords in a Mariadb 
database that is managed by Postfixadmin. I used the following 
settings for backents.local.php.

<?php
$backends['postfixadmin']['disabled'] = false;
$backends['postfixadmin']['policy']['minNumeric'] = 0;
$backends['postfixadmin']['params']['phptype'] = 'mysqli';
$backends['postfixadmin']['params']['password'] = 'deleted';
$backends['postfixadmin']['params']['encryption'] = 'md5crypt';
$backends['postfixadmin']['params']['show_encryption'] = true;
$backends['postfixadmin']['params']['query_lookup'] = 'SELECT password 
FROM mailbox WHERE username = %u and active = 1';
$backends['postfixadmin']['params']['query_modify'] = 'UPDATE mailbox 
SET password = %e WHERE username = %u';

When I try to change passwords, I get the following message: Failure 
in changing password for Postfix Admin server: Incorrect old password.

Horde.log shows the following error:
2016-10-22T10:05:23+00:00 NOTICE: HORDE [passwd] PHP ERROR: Undefined 
index: db [pid 2902 on line 113 of 
"/usr/local/share/horde/passwd/lib/Factory/Driver.php"]
2