Here is a small post on how to setup pflogsumm on your CentOS mail server running Postfix.  It takes advantage of logrorate being called nightly by cron.
1. Install pflogsumm

# yum install postfix-pflogsumm

2. Run a test

# /usr/sbin/pflogsumm /var/log/maillog

3. Update /etc/logrotate.d/syslog.  Add the following:

 prerotate
    /usr/sbin/pflogsumm /var/log/maillog | mail -s "Postfix Logs Summary `date`" your-email-address
 endscript