Index and analyzer are used by the full-text search engine.
Standard analyzer for indexing by default. You should choose the
language you used most in emails, so that Spider can pick up the best analyzer
for this language and get most accurate search result after indexed. If your
language is not listed on the dropdown menu, then simply use the default
After changing the language, all indexed messages will be reindexed automatically and immediately, it may take a while to finish. Searching during reindex may not get full result until reindexing finished.