Hi Nadia,
This is more a fetchmail-question. Why should this be more complicated than the way you used it with the Zarafa-unix-plugin ?
When using the DB-plugin in a Multi-company-setup, format of the SME/unix-username and the ZARAFA-username has to be [username].[companyname]. SME itself doesn't 'know' companies, only users and groups. So, for SME it doesn't make a difference if you have more than one company in Zarafa.
Can you explain where you are confused ?
F.