Kolab3.0beta/Debian: Sending mail from Roundcube fails

Hi *!

Just ran into another problem with the test server (Kolab 3.0beta with 
updates/Debian Wheezy): When trying to send mail from Roundube, I get a "SMTP 
Error (535): Authentication failed." error message.

Looking at mail.log, I noticed the following initially:

Dec  4 18:05:54 SERVER postfix/submission/smtpd[5750]: warning: SASL 
authentication problem: unable to open Berkeley db /etc/sasldb2: Permission 
denied
Dec  4 18:05:54 SERVER postfix/submission/smtpd[5750]: warning: SASL 
authentication failure: unable to canonify user and get auxprops
Dec  4 18:05:54 SERVER postfix/submission/smtpd[5750]: warning: 
localhost[127.0.0.1]: SASL DIGEST-MD5 authentication failed: generic failure

I found that I could get rid of this by adding postfix to the sasl group, so I 
tried that as an experiment. Now I get:

Dec  4 18:29:58 SERVER postfix/submission/smtpd[3526]: connect from 
localhost[127.0.0.1]
Dec  4 18:29:58 SERVER postfix/submission/smtpd[3526]: warning: SASL 
authentication failure: unable to canonify user and get auxprops
Dec  4 18:29:58 SERVER postfix/submission/smtpd[3526]: warning: 
localhost[127.0.0.1]: SASL DIGEST-MD5 authentication failed: authentication 
failure
Dec  4 18:29:58 SERVER postfix/submission/smtpd[3526]: disconnect from 
localhost[127.0.0.1]

So that change didn't do much... Sending mail from the server itself (e.g. as 
root using "mutt") works fine.

Any ideas where to look?

Thanks in advance,

Thomas
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           Thomas Ribbrock, IT-Team brightsight