On system were the default shell is not bash, the autoresponder script can fail on existing installations, as the existing /etc/kopano/autorespond config file still contains a bashism, while the autoresponder has been switched to use /bin/sh.
This will not occur no fresh installations where the new config is already correct.
Error in /var/log/kopano/server.log as follows.
[debug ]  /usr/sbin/kopano-autorespond: /usr/sbin/kopano-autorespond: 83: /usr/sbin/kopano-autorespond: arithmetic expression: expecting primary: "1491919710+$"
Existing config file
# Only send reply to same e-mail address once per 24 hours TIMELIMIT=$[24*60*60]
Fixed config file
# Only send reply to same e-mail address once per 24 hours TIMELIMIT=$((24*60*60))
Please see https://jira.kopano.io/browse/KC-967 for more information.