Edit the imta.cnf file.
The file is located in the /opt/SUNWmsgsr/config directory.
To enable logging for a particular channel, add the logging keyword to the channel definition. For example:
channel-name keyword1 keyword2 logging
In addition, you can also set a number of configuration parameters such as directory path for log files, log levels, an so on. See 25.4 Managing Message Store, Admin, and Default Service Logs
The message return job, which runs every night around midnight, appends any existing mail.log_yesterday to the cumulative log file, mail.log, renames the current mail.log_current file to mail.log_yesterday, and then begins a new mail.log_current file. It also performs the analogous operations for any connection.log* files. It is possible that mail.log_yesterday contains time stamps which have already passed over rotation time.