(I work for Fastmail). I'm not quite sure what to make of this. We believe our search is generally as powerful as Gmail's, and in some ways more so (see all the things we support here:
https://www.fastmail.help/hc/en-us/articles/360060591213-Sea...), but we're always happy to hear ideas for improvements.
> no partial matches
To make your search fast, we use an index. This means we match on stemmed whole words by default (so a search for "bus" would match "busses", but not "business" for example). We also support prefix matching, if you end with a `` (e.g. "bus" would match both "busses" and "business"). We cannot support pure substring matches. This is exactly the same as Gmail as far as I can tell (although their stemming algorithm is probably slightly different). Gmail also doesn't support prefix searches as far as I know, just stemmed whole word matches.
> no matches for spelling mistakes
I see if your result has no matches in Gmail, it applies spelling correction and shows you what results this produces instead — I agree, this is a nice feature, I'll add it to our ideas bank.
> weird indexing of some sort of email content (attachments?) that leads to a match when there is absolutely nothing related in that email
We index the contents of attachments (again, as does Gmail I believe). By default we search everywhere, including inside attachments if you just search for a word. Most users find this helpful. If you want to restrict to just searching the message content, you can do so with the `body:` operator.
> it has no idea about the context of the search to improve matches, like 'flight' being possibly related to e.g. travel
I'd love to hear more about how you expect this to work. Searching a Gmail account on the web for "flight" doesn't seem to do anything special I can see, but maybe it does so in their app?