There was a time, long, long ago, when mail from your email provider to your recipient's provider would often go through other providers in transit. Nowadays (and for the last 20 years) all of the intermediary mail-servers in the Received: headers belong to either the sender's provider or the recipient's provider. They're usually spam-filters, application gateways, secondary servers.
I guess the major exception is people who use gmail or Mailchimp as an outbound relay. But that's deliberate, and entirely under the sender's control.
And the article linked from their article (hilarious itself) pointed out that this basically comes down to State Actors (Mossad as the example) or Everyone Else. If it's Mossad then there's nothing anyone else can do to protect you (because they can do secret-squirrel things through special security courts and stuff like installing black boxes on undersea cable routers). If Everyone Else, then the normal run-of-the-mill transport encryption is probably good enough, just don't click on any herbal boner-pill adverts.
tldr; If you want to be protected, you have to do PGP at the local machine level yourself.
[0] Given that Fastmail are Aussies, and that our idiotic government have given the spooks full, secret, access to anything they want, then this is a very real prospect for anyone that five-eyes might be interested in.
This is oversimplification if not misleading. There are also Bad Guys (who aren't state actors), who usually can't reach for your data. But occasionally they can, when rare Planet Parades like Heartbleed or Meltdown make the news. And they are happy to use this one-in-a-lifetime chance to sell access to your data to everyone else.