SMTP delivery with multiple recipients

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http://serverfault.com – I'm going over some SMTP log files from an open relay server (IIS 6 SMTP Virtual Server), used to collect and route all automated email within a private network, to an internet smarthost (qmail at another ISP). Using SawMill 8.5 to parse the logs, it appears that there is a big difference between the number of messages delivered from my server, and the number of emails that the internet smart host sends out. For a period where I have delivered 2000 emails to the smart host, the smart host has delivered 3000 emails to the internet. I guess this has something to do with emails having multiple re (HowTos)