Time to check the rate limits on your mail servers

CNET reports http://news.com.com/Zombie+trick+expected+to+send+spam+sky-high/2100-7349_3-... that botnets are now routing their mail traffic through the local ISP's mail servers rather than trying their own port 25 connections. Do you let your customers send an unlimited number of emails per day? Per hour? Per minute? If so, then why? --Michael Dillon