just update roundcube
yum update --enablerepo=stephdl
after that you have 2 plugins which are able to manage sieve and therefore vacation
managesieve (provided in the bundle) and sieverules provided by composer
config setprop roundcube PluginsList globaladdressbook,calendar,libcalendaring,contextmenu,markasjunk2,vcard_attachments,newmail_notifier,emoticons,tasklist,managesieve
or
config setprop roundcube PluginsList globaladdressbook,calendar,libcalendaring,contextmenu,markasjunk2,vcard_attachments,newmail_notifier,emoticons,tasklist,sieverules
and
signal-event roundcube-update