Using a Macro to send data to shared Outlook Calendars

You can use the Namespace.GetSharedDefaultFolder method to access the Calendar folder in another Exchange mailbox - as long as you, or more to the point, the current user has permissions (in Outlook) to do so.

Code snippet - this temporarily creates an email message so it can resolve the addressee to get the correct calendar

    strName = "DoeJ"
     
    Set oApp = CreateObject("Outlook.Application")
    Set oNS = objApp.GetNamespace("MAPI")
    Set oDummy = objApp.CreateItem(olMailItem)
    Set oRecip = oDummy.Recipients.Add(strName)
    oRecip.Resolve
    If oRecip.Resolved Then
        On Error Resume Next
        Set oFolder = _
          oNS.GetSharedDefaultFolder(oRecip, _
            olFolderCalendar)
        If Not oFolder Is Nothing Then
            Set oAppt = objFolder.Items.Add
            If Not oAppt Is Nothing Then
                With oAppt
                    .Subject = "Test"
                    .Start = Date + 7
                    .AllDayEvent = True
                    .Save
                End With

Partial code only to illustrate the idea, that will not compile.