I want to use logrotate which is standard with RH5.2 Linux to rotate my mail logs. Anyone worked out the logrotate config file that will do this?

Here's one suggestion:

/var/log/exim/main.log {
    create 644 exim exim
    rotate 4
    compress
    delaycompress
}

The sleep is added to allow things to close the log file prior to compression. You also need similar entries for the panic log and the reject log, of course.