Mbox is not that easy to process, especially if 1986 time span is taken into account. There is base64 encoding. There is "=" encoding, don't recall whats its name. "Equals" encoding. There are several character encodings if 1986 time span is taken into account, and each character encoding will be encrypted by equals signs. There was KOI8-R. KOI8-R was on BSD and Linux servers, but desktops had cp1251, so 1251 entered e-mail eventually, via e-mail clients autoconfigured to desktop encoding, or via webmail interfaces autoconfigured to web encoding which could likely be cp1251 and not likely koi8-r. Then utf-8 came in.