Setup Postfix with SMTP-AUTH over SASL2 with SASLDB for users to send emails
Solution 1:
If anyone got the same error this maybe save you from hours of searching.
In order to use sasldb you need to change the MECHANISMS="pam" line to MECHANISMS="sasldb" in the file /etc/default/saslauthd, that was what I missed.
Then restart the saslauthd and the postfix, and it works with the configuration above.