Check Point has recently released a very helpful MTA Debugging and Performance Troubleshooting Toolkit (sk120260).
This Toolkit is intended to help identify and debug problems in the MTA components and e-mail flow through the MTA (such as e-mail latency, e-mails not reaching their destination, etc.).
MTA Performance Troubleshooting Guide.pdfguide
Debugging Email Flow in Gateway Configured as MTA.pdfguide