We install ZImbra 8.6.0_GA_1153.FOSS on Ubuntu 12.04.5 LTS, while checking the reports i found higher number of send mail from username as "from=<>". How could I know which machine generate this message? I gone through the logs but unable to found any clue on sender detail. I found the receiver details. but was not able to find sender detail. Is there any way to find the detail?