I am a psychotherapist and legally required to ensure confidentiality. I rarely send out an email to more than one client at a time, but I had an occasion to do so today. Fortunately, I tested the system ahead of time (using three email addresses that come directly to me) and discovered that no matter what I did or didn't do, all the email addresses were disclosed. If this had never worked this way in the past, no one would expect it to now. But when a highly useful feature is eliminated, that is a definite failing. Several years ago, the consensus advice was to NOT use bcc because either some ISPs or individuals would treat those emails as spam.
I used Eudora for years before changing to Mac and found it much better overall. But with an integrated system, using the Mac mail along with its contacts and calendar, is more streamlined. As for sending Apple a message about email, I've done that with other issues in the past. The messages seem to drop into a black hole, perhaps on their way to a whole different universe, but not having an impact in this one.
While this may not be exactly "on message" for this specific topic, I discovered that Apple has made another frustrating elimination with Safari. I use the open a duplicate of the page option all the time (if I'm copying a reference and doing a search by Google so I don't lose the original page nor get a long ways out from prior pages; etc.). Well, it is gone and no longer an option on the "customize the toolbar" selection. Why? I did find another version to add into Safari. All of this eats up time; or if one has a touch of ADHD, a lure out into the finite universe of links. Now, if all of us were adept programmers, no worry. (Or if, in sf fashion, we could just snap on a chip.)