Message Tracking vs SMTP Protcol Logging in Exchange 2007

Message tracking
 Is a feature that you can use to track messages across an Exchange organization. You can track all types of messages, including system messages and regular e-mail messages that are going to or coming from a non-Exchange messaging system. You can use Message Tracking Center to locate messages that failed to arrive in your users' mailboxes, such as messages that are stuck in the message queue.
Message tracking is enabled by default in exchange 2007. You can modify the length of time log files are kept and increase logs directory size. The default period that tracking logs are kept is 30 days.
Protocol Logging
When you keep a history of all SMTP protocol activities, you can prove whether a particular message left your server, verify whether the SMTP virtual server is performing its work as expected or is experiencing communication problems, and identify attacks from the Internet.
Protocol Logging isn’t enabled by default on exchange 2007. Logging needs to be configured for the send and receive connectors. You can modify the length of time log files are kept and increase logs directory size. Default age period is set to 30days, but can be increased.