Sieve & ISPConfig 3.1: Mark messages as read
Sieve requires imap4flags for that purpose.
Custom config file template for Sieve
cp /usr/local/ispconfig/server/conf/sieve_filter_1.2.master /usr/local/ispconfig/server/conf-custom
Add imap4flags
vi /usr/local/ispconfig/server/conf-custom/sieve_filter_1.2.master
require ["fileinto", "regex", "date", "relational", "vacation", "imap4flags"];
Add custom mailfilter reciepe to ISPConfig
setflag "\\seen";