Historical inbox summaries named by date (YYYY-MM-DD-daily.md, YYYY-WW-weekly.md). Each digest contains: priority threads requiring action, important updates grouped by sender/topic, and a quick-scan summary. Create new file per digest period—never overwrite past digests as they serve as searchable history. Keep last 30 daily and 12 weekly digests; archive older ones. Reference past digests to identify patterns or find "that email from last month." Don't duplicate full email content—summarize and link to thread IDs.