Notes are stored as messages in a dedicated Notes folder/mailbox on the IMAP or JMAP server, keyed by the RFC 2822 Message-ID header via the X-SharedInbox-Note-For custom header. This survives folder moves since Message-IDs are stable. Multiple users sharing one account see the same notes. A local Drift cache (schema v39, EmailNotes table) is kept in sync on demand when the email detail screen is opened. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>