imap auth method CRAM-MD5 with LDAP

==== Required information ====
- iRedMail version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Linux/BSD distribution name and version:
- Related log if you're reporting an issue:
======== Required information ====
- iRedMail version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Linux/BSD distribution name and version:
- Related log if you're reporting an issue:
====

Hi, I purchased a license earlier this year, and am about to migrate a lot of accounts to iRedMail-Pro with LDAP.

Many existing clients are set up with CRAM-MD5 authentication, which i need to be able to support when migrating to iRedMail.
We have written our own migration script based on your create_mail_user_OpenLDAP.py, but adding domains, aliases, groups and catch alls. So far so good. We migrated the userPassword attribute in plain text.

- I can log in through iredadmin and through roundcube with all imported accounts
- I can log in via imap via "Login" (Plain) with MUAs
- I cannot log in via CRAM-MD5.

What I tried:
- Changed in dovecot.conf:

auth_mechanisms = PLAIN LOGIN CRAM-MD5 SCRAM-SHA-1
auth_debug = yes

The output of the log is:

Sep 30 00:39:20 auth: Debug: ldap(user.name@example.com,xx.xx.xx.xx,<xxxxxxx>): passdb doesn't support credential lookups

From what I can see, your LDAP schema is already set up in a way so that dovecot can read the userPassword.
The userPassword in the LDIFs was imported without any {} prefix, like this:
userPassword: blabla

Any help would be greatly appreciated. We are planning an even bigger migration after the current one (with a new license), if all succeeds well.

Thank You in advance for any hints on how to resolve this issue.

Lorenzo

==== Required information ====
- iRedMail version: 0.8.7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Linux/BSD distribution name and version: FreeBSD 10
- Related log if you're reporting an issue:
====