@mstadmin
#Yacy allows searching any #Mastodon post from any server.... IF it has crawled it. I have my server set up to crawl certain feeds on a schedule, so the search results will be up-to-date. And Yacy is not for Mastodon only, but for any web page that has been crawled.
Regarding #Elasticsearch, is that a search option available on your Mastodon instance but requires you to be logged in to use it? You can search only your posts, and not those from other accounts, right?
