Postfix not writing to mail log files on wheezy system.

[peter green <submission2013@arsr-swicom.org.uk>]

While attempting to look into a mail issue on one of my machines I 
noticed that /var/log/mail/mail.log did not appear to have been updated 
since december.

I belive that this may have been triggered by an upgrade from squeeze to 
wheezy but I don't remember exactly when I upgraded the machine.

Any thoughts on how to go about troubleshooting this?