Postfix: master_wakeup_timer - connection refused

I have a new installation of Plesk version: 12.5.30 Update #52 on Ubuntu 14.04.5 LTS‬ on a vps from OVH

my Mail.log is stuffed with errors:
postfix/master[1662]: message repeated 4 times: [ warning: master_wakeup_timer_event: service pickup(public/pickup): Connection refused]
postfix/master[1662]: warning: master_wakeup_timer_event: service qmgr(public/qmgr): Connection refused
postfix/master[1662]: warning:...

Postfix: master_wakeup_timer - connection refused