Queue file write error, invalid file rights

After upgrading from 3.0 to 3.1 there are errors in mail.log

Temporary MTA failure on relaying, from MTA(smtp:[127.0.0.1]:10025): 451 4.3.0 Error: queue file write error (in reply to end of DATA command
warning: mysql:/etc/postfix/mysql-virtual_outgoing_bcc.cf is unavailable. open /etc/postfix/mysql-virtual_outgoing_bcc.cf: Permission denied

This is due to invalid access rights for the newly created files (rw - - instead of rw r -).