Is there anything that would, to take a very simple example, if I emailed “johnsmith@abc.com” … and I searched for emails including “John Smith” – return me that email?
Or to be able to search for a word and it recognizes synonyms if I want it to?
Or to be able to some kind of useful natural language type searching (“any emails that involve payments from Tina”).
I mean there are so many ways email search could be far, far more powerful.
Anything out there?
Mail.app has decent search but, depending on your email provider, you might find webmail is much better.
For me, a major fault of the Mac is that the Mail database isn’t wired into the system search (Spotlight). If a Spotlight search found Mail then all sorts of complicated searches would be possible. Ironically, I’ve got old (like 20+ year old) mail from a program called PMmail that Spotlight searches just fine because messages were stored in individual text files.
If you have DEVONthink and import your mail into that, you can have complicated searches.
It used to be, and Apple says “When you search your Mac using Spotlight, emails are included in the results. You can exclude them by changing Spotlight settings.”
But it hasn’t worked for me in years.
I’m on macOS 13.6.4 and being suprised at your comment, I did a search just now with Spotlight and it found mails for the words I search for (inside a mail message) and Spotlight found the email. I didn’t do any more tests than that.
Is that Pegasus Mail, by chance?
I just tried it again and it seems to find some things in mail, but not all. No idea why it is so inconsistent. And that takes Spotlight Search from the menu bar or keyboard shortcut. Spotlight Search in the Finder doesn’t see mail at all, and only it allows complex searches.
“PM” stood for Presentation Manager. This was originally an OS/2 Mail Program and I used OS/2 for a great deal of the 90’s. They did come out with a Windows version that I used for a while. The basic problem with the program was that it was strictly ASCII text messages. With the whole world seemingly going to Outlook, messages were always HTML format and only sometimes had plaintext attachments. This made PMmail hard to use.
Mail.app’s hit-and-miss search is the main reason that I moved away from it. I’m currently evaluating MailMate and pretty certain I am going to move to it. I’ve found the search to be incredibly reliable and I can at last “understand” what is being searched for (see the modifiers under “Search View” in the manual here). It’s not intelligent search / NLP like you are after, but it’s the closest to mutt’s search which I used to rely on.
How about that, you are correct. Spotlight can find email messages if you search from the menu bar, which I never do. But not from the Finder.
Mail’s search function is so irritating I’ve pretty much abandoned it (I manage a lot of inboxes and faffing about with their crap search is a hassle I don’t need). I’ve been dissatisfied with Gmail’s search too, and my solution was to archive all the mail I could in DT. It solved the problem for me since now I just use DT’s awesome search.
This also has the added benefit that it removed most the historic emails from the inboxes, which made both Mail’s and Gmail’s search functions a little better since they’re searching a far smaller number of emails.
Mac Mail is ‘wired into’ Spotlight for me. This is how I do most of my email searching. Working great!
When searching on this topic, there are the Canary Mail client seems to be orienting on this:
Note that this is stated as a ‘next feature to implement’, and not being readily available.
I do not have any experience in using Canary Mail, as I am still a happy MailMate user 
The excellence of its search is why I continue to use Mailmate. I think I’ve been using it for about a decade. I have multiple email accounts and 20 years of email data and I can always find what I’m looking for.
However, it’s an investment of time to set up Mailmate. I’ve personalized my keybindings and love that I can power through my email so quickly, but it took a while to learn how to do it.
And search is my favorite feature. I run a zillion searches a day that look something like “f andy d 2w” which translates to “search from messages that contain “andy” in the from field and were received in the past 2 weeks.”
See the table of search terms here:
https://manual.mailmate-app.com/view
If only Canary was more polished it’d be the perfect client across all Apple devices! Maybe one day