Hi,
You can use grep command as below
grep "Mar 31" mail_logs
The ISQ notification is generated the appliance on which spam quarantine is configured, it could be the ESA if local quarantine is enabled or the SMA if centralized spam quarantine is enabled.
Comprehensive Spam Quarantine Setup Guide on Email Security Appliance (ESA) and Security Management Appliance (SMA)
http://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/118692-configure-esa-00.html
Thank You!
Libin Varghese