Get SMTP Auth user name in Exchange 2007?

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Hello, all.

When implementing SmtpReceiveAgent I have a lot of events to catch such as OnAuthCommand, OnConnect and so on as described in
http://msdn.microsoft.com/en-us/library/aa494203(EXCHG.80).aspx

Could someone please point me which of these event I need to obtain the information on which user name was used to authentificate SMTP session?
Thanks.

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