I agree that (1) a return receipt feature would be nice, (2) that receiving email with a "return receipt" demand is annoying, (3) a return receipt that the recipient can decline AND read the email is worthless.
Thunderbird, which looks like a much smarter free client than Apple Mail, allows you to request a receipt on a case-by-case basis. I agree setting it globally makes one look rather overly anxious. Also, I'm not sure Apple Mail even honors incoming receipt requests!
I want something that works like old-fashioned certified mail: the recipient can sign for and read or decline and NOT read the message. I get date-stamped notice either way. It might also send you a notice that an email has not been picked up after a certain interval and has presumably been lost. This addresses the lost-mail scenario and is useful in the situation where the recipient pretends not to receive emails and blamed the sender (as you might suppose, a phone call is not a good alternative with such a person). The who-said-what-when can be invaluable, not just in litiagtion contexts but in figuring out where communication broke down so that it doesn't happen again. The log should be created automatically.
So, no email client can really fix this. (Apple mail should still have the option to request receipt!) The only way I can see for this to work is to go through a 3rd party. Ideas?
For now, yes, request a reply when it's important!!!!
One alternative I hate to mention is the "bug" the emails. Services such as didtheyreadit embed invisible images or html tricks in emails and report back every time the message is opened or forwarded, including time, date, IP address, and other details. Maybe this doesn't break the law in that it doesn't reveal private information about the person's computer etc. any more than their picking up the phone does, BUT I dislike it and think the recipient should, as with certified mail, have a chance to decline seeing the message altogether. Perhaps one could bug AND advise the recipient that you do so. At least it is automatic and provides a 3rd-person log that you can point to in a dispute and not be accused of fabricating. Not that I know personally, ahem, but it does work quite well provided the recipient doesn't know how to block it. Admissible in court? I'm not sure.