Lists stopped at what the first sync brought in: the newest 300 inbox
messages on IMAP, the last 30 days on Microsoft 365, and a folder's
newest 200. A new load_older command reaches 100 messages further back
in the inboxes and folders a list shows, through each account's worker
round, and resolves once those rounds are over. Accounts and folders
say whether there's more (hasOlder).

On IMAP the inbox fetches the next UIDs below its floor and lowers it,
so later syncs track that mail like the rest; a folder raises its
window and downloads only what it didn't have. On Microsoft 365 the
inbox lists mail received before the delta window, and a folder pages
its listing up to its new limit, fetching bodies only for the stretch
that's new. Older mail arrives quietly: no notifications or screening.
Mail older than the Microsoft 365 delta window doesn't pick up changes
made elsewhere afterwards.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>