The SentOn property specifies the date and time that the message is sent.
Property SentOn as Date read-only HRESULT get_SentOn(DATE* pVal);
The SentOn property is determined from the Date header field of the message. This value is also accessible using the urn:schemas:mailheader:date or urn:schemas:httpmail:date fields.
Both the IMessage.SentOn and IMessage.ReceivedTime properties return the time offset to the time zone defined by the urn:schemas:calendar:timezoneid field in the associated Configuration object. If no time zone is specified, no offset is performed and the date and time are returned in coordinated universal time (UTC).