The email schema is indirected. The actual email data is not in the PIRDE tables, it's referenced from them. This is a performance hit, but a huge flexibility win. Let's call the data an indirected PIRDE schema is based on a "basis". The PIRDE email schema assumes one or several unix mailx-format mail folder files as it's basis. The email schema command "index" generates or updates 3 PIRDE tables based on the basis, namely "messages", "people" and "contacts".
With those 3 tables indexing the actual data you have a lot of ways to look at it. The "messages" table has pointers to the mailx synopsis key, From:, Subject:, and main body offsets of each email. This is a typical email message in mailx format...