68K Macintosh user agent is ancient! Pre Y2K.
Assuming the headers aren't spoofed. I think some of them are. see http://www.zytrax.com/tech/web/browser_ids.htm, which, I think, explains this as "Life behind a junkbuster proxy."
Fudging e-mail headers is what spammers do to get past various anti-spam facilities. Other than the "last hop," the header information is not reliably provable by a recipient.