Defaulted to true. If true then changes made to the message object in pre:receive will be saved in the session history for the length of the session. If the changes are saved then the message will look the same to the end user before and after page change/reload as long as the session history feature is enabled. If updateHistory is false the changes will not be saved in the history. While the message will still initially update successfully if this is false, the changes won't be preserved and the end user will see the original message (that was received before the pre:receive changes) when a page change/reload occurs.
The type of this event.