mu4e is fully search-based: even if you ‘jump to a folder’, you are
executing a query for messages that happen to have the property of being in a
certain folder (maildir).
Normally, queries return up to
mu4e-headers-results-limit (default: 500)
results. That is usually more than enough, and makes things significantly
faster. Sometimes, however, you may want to show all results; you can
enable this with M-x mu4e-headers-toggle-property, or by customizing the
mu4e-headers-full-search. This applies to all search commands.
You can also influence the sort order and whether threads are shown or not; see Sorting and threading.