Hi there. - Linux Distribution and version used on your server - Debian 8 - ISPConfig version - 18.104.22.168p9 The problem is basically connected with mysql and postfix. On two servers I've faced this problem, however I'm running multiple ispconfig servers under same version and so far no problems there. In the mail log you can see the following: Because of that there is Server configuration error since lookup table fails - mail server is not working and you can't send emails. Before restarting any services I've tried to log in manually to mysql using user root and ispconfig user in that file = no problems at all. Mysql was showing historical max connections ever used 34 - which is maybe 10% of the max connections defined. Any idea why mysql is rejecting connections, even though I can log in manually and user limit is not reached? Mysql error log is not showing anything apart from "can't connect" from postfix.