Yeah, this is the version I remember also. PB has said many times that he built the first version that could only display threads of his own email in a day. But

Yeah, this is the version I remember also. PB has said many times that he built the first version that could only display threads of his own email in a day. But going from a series of raw email messages to an email thread that can be displayed conversationally on the web is a multi-year project, so clearly there was some already existing code doing the heavy lifting. E.g. the email parsing code in Thunderbird dates back to at least the late 80s, and even after decades of working on it at a cost of hundreds of millions of dollars, it's still a work in progress.