Not overkill at all, but youy should know that there are a lot of competitors in the e-discovery software category, and they do a lot besides classification, starting from the ingestion of email archives, through extraction of attachments (recursively, because Outlook PSTs get mailed as attachments too), identifying and attributing quoted text, deduplication of messages and documents, SNA, clustering, normalization, canonicalization, NER, synonym identification (aside from correctly identifying people referred to by nicknames, advanced implementations can also figure out when people are using a code-word to evade filters), etc.