...for items such as viruses, profanities and bandwidth draining media, had to be manually monitored to ensure that legitimatemail had not been incorrectly quarantined. It would take several man hours every single day to go through the logs...
http://www.securitypark.co.uk/security_article263668.html
...client zombies or any evidence of legitimatemail being rejected by the client...Gmail that may send a mixture of legitimatemail and spam. It also works well...commercial bulk mail) and some legitimatemail is quarantined, but the volume...
http://www.escom.com/ASMTP_wp.pdf