Most of the time I just use the Fastmail web browser interface. I can access it over IMAP with Thunderbird butt it’s noticably slower. Depending who your email provider is you may find they have an acceptable web interface.
I have tried the search, for example !space doesn't return anything - but if I try @space or [email protected] I get the response not found. Maybe I need to wait longer for the search to query the remote instance @lemmy.link?