Fix Dovecot namespace inbox=yes for CentOS 7

Co-Authored-By: dpeca <dpeca@users.noreply.github.com>

install/vst-install-rhel.sh

@@ -1127,6 +1127,9 @@ if [ "$dovecot" = 'yes' ]; then
     cp -rf $vestacp/dovecot /etc/
     cp -f $vestacp/logrotate/dovecot /etc/logrotate.d/
     chown -R root:root /etc/dovecot*
+    if [ "$release" -eq 7 ]; then
+        sed -i "s#namespace inbox {#namespace inbox {\n  inbox = yes#" /etc/dovecot/conf.d/15-mailboxes.conf
+    fi
     chkconfig dovecot on
     service dovecot start
     check_result $? "dovecot start failed"