Problems using imapauth with OX and dovecot

[Volker79]

Hi there,
we installed an ox server on debian jessie, version 7.8.1-11.
Our mailclients are based in a mysql database from postfixadmin.
Imaplogin and sasl via imap is running fine with mailclients.
Now we use to configure ox app suite, to login with emailaddress via imap.
We get the error: "The user name or password is incorrect. (LGI-0006)"
We tried configuration from http://oxpedia.org/wiki/index.php?ti...in_description

Our configuration details at the moment (tried other options, too)
imapauth.properties:
USE_FULL_LOGIN_INFO=false
USE_FULL_LOGIN_INFO_FOR_USER_LOOKUP=false
USE_MULTIPLE=false

mail.properties:
com.openexchange.mail.loginSource=mail

In the logfile we didnt see a reason and a login attempt isnt seen in the dovecot or mail logfile.

2016-05-18T13:31:46,173+0200 INFO [OXWorker-0000007] com.openexchange.login.internal.LoginPerformer.log LoginRequest(LoginPerformer.java:651)
Login:xxx@xxxxx.de IP:37.208.xx.xx AuthID:bfd62dcd74ea4c8aaa45424c998e9378 Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:45.0) Gecko/20100101 Firefox/45.0 Clientpen-xchange-appsuite(7.8.0-19) Interface:HTTP_JSON No session created.
com.openexchange.grizzly.method=POST
com.openexchange.grizzly.queryString=<none>
com.openexchange.grizzly.remoteAddress=37.208.xx.x x
com.openexchange.grizzly.remotePort=60879
com.openexchange.grizzly.requestURI=/ajax/login
com.openexchange.grizzly.serverName=ox-xx.xxxx.de
com.openexchange.grizzly.servletPath=/ajax/login
com.openexchange.grizzly.session=67126809108690715 3.APP1
com.openexchange.grizzly.threadName=OXWorker-0000007
com.openexchange.grizzly.userAgent=Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:45.0) Gecko/20100101 Firefox/45.0
com.openexchange.login.authId=bfd62dcd74ea4c8aaa45 424c998e9378
com.openexchange.login.client=open-xchange-appsuite
com.openexchange.login.clientIp=37.208.xx.xx
com.openexchange.login.login=xx@xxxx.de
com.openexchange.login.userAgent=Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:45.0) Gecko/20100101 Firefox/45.0
com.openexchange.login.version=7.8.0-19
com.openexchange.request.trackingId=a23ad534399143 0e92d24c7989508412

Any ideas what we can check or whats going wrong?

Regards,
Volker