MailItem first modification time

I would like to capture date and time when an email was FIRST modified after its creation (e.g. a category tag was added to it). Is it possible to add a FirstModificationTime property to MailItem object - similar to the existing LastModificationTime? How to do it? Any help will be appreciated.

You could add a User Property.

With FieldChooser | User-defined fields, you can manually create the user-defined field FirstModificationTime or once you run this you can add the automatically created field to the folder view.

Sub UserProp_FirstModificationTime()

    Dim myItem As mailitem
    Dim myUserProperty As UserProperty

    Set myItem = ActiveExplorer.Selection.Item(1)
    Set myUserProperty = myItem.UserProperties.Add("FirstModificationTime", olText)

    ' If you use a trigger event for this it will update once only.
    If myUserProperty.Value = "" Then
        myUserProperty.Value = Now
        myItem.SAVE
    End If

End Sub