+ num INTEGER NOT NULL, /* NNTP article number == IMAP UID */
+ tid INTEGER NOT NULL, /* THREADID (IMAP REFERENCES threading, JMAP) */
+ sid INTEGER, /* Subject ID (IMAP ORDEREDSUBJECT "threading") */
+ ts INTEGER, /* IMAP INTERNALDATE (Received: header, git commit time) */
+ ds INTEGER, /* RFC-2822 sent Date: header, git author time */
+ ddd VARBINARY, /* doc-data-deflated (->to_doc_data, ->load_from_data) */