[exim] How to rotate exim file using cron

Hello,

I want to setup a cron to rotate exim file with a backup file every 7
minutes. But the cp command doesnt seem to be working.

I use

35    *    *    *    *    /bin/cp -f /etc/exim.conf6 /etc/exim.conf; service
exim restart;
42    *    *    *    *    /bin/cp -f /etc/exim.conf7 /etc/exim.conf; service
exim restart;

but this does not work and old version of exim.conf still remains there. I
thought over writing may be an issue so I used

4    *    *    *    *    service exim stop;yes | cp -f /etc/exim.conf4
/etc/exim.conf; service exim start;

again that did not work.

What am I doing wrong