Is it just me?
I search for (ironically) a Fastmail ticket number, and the results are missing a bounce message containing that number in its bounced message's Subject. (Gmail fails likewise.)
You'd hope you could workaround by searching instead for a match in the body, and it sometimes works. But it sometimes fails, because contrary to FM bounce text saying the message is attached, its body is sometimes missing. Support: "There are certain scenarios where a bounce in the forwarded email can result in only headers being attached to the bounce and not the full email." and including the intact message "with the current setup this is not trivial to do"