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 recipients. So my question is this:
When does a single message with multiple recipients get split and routed to the individual recipients' MX? At submission? At the last hop before the internet? Or is this MTA specific?
Let me now if I need to clarify anything