Can't send mail to shared folders: kolab+shared.archiv at domain.tld

[Alexander Maret-Huskinson]

Hello list,

we have a kolab 2.0.1 installation running, upgraded from version 2.0 beta4. I 
don't know if it ever worked, but I can't send mails to shared folders. I 
have created a shared folder named 'archiv' and if I want to send a mail to 
'kolab+shared.archiv at domain.tld' postfix says:

550 <kolab+shared.archiv at xxxxx.xxx>: Recipient address rejected: User unknown 
in local recipient table (in reply to RCPT TO command))

It seems that postfix doesn't know about a user 'kolab'. At first we had a 
group account named 'problems' with the address 'kolab at ...' assigned as an 
e-mail alias and all mails to 'kolab+shared... at ....' were delivered to this 
account. We removed the alias 'kolab at ...' from the account and now we get the 
above error message from postfix.

What do I have to do to get postfix to recognize kolab as a user again.

Can anyone help?

Greets,
Alex