Once upon a time, mail delivery was a ritual. The postman with his bike and whistle, the big red post boxes, the letters that went all the way around the world on a boat... I still can't get over the way postmen in the UK actually push your mail through the letter slot in your front door! (Maybe that doesn't happen any more?)
Then more and more people used mail for other things, like trying to sell you stuff, and advertising things you didn't want, and sending a million Christmas cards. The postal service suffered overload and efficiency went down. Or did it? Maybe we just expected too much. Letters were lost. Parcels went astray. But not always. I still remember a birthday present my grandmother sent to me in Sydney years ago - in the days when I moved around a bit - and I think it went back and forth across the Tasman Sea four times before I finally got it, covered in crossed out addresses and new attempts to find me.
I live in an area that seems to have a sub-post office. This means that if someone in the delivery area is running late (most days), my area has to wait for the next day. I complained. Huh! I've got used to receiving things a day later than everyone else. But my postman has been on the job for years, so wrongly-addressed letters often still get to me. The thing is - letters still go astray, even important letters. A few years ago, I sent 150 pages of a manuscript that I'd edited back to a writer friend. Admittedly, she was in Queensland at the time, but at a legitimate address. She never received it. Recently, an edited manuscript sent to me never arrived. Where on earth do these things go? It's not as if they're in small envelopes!
But woe is you if you think email is any better. By my estimates, at least 3% of my emails either never reach their destination, or I never receive those destined for me. When it's someone asking if I've read a review in the weekend paper, I'm not likely to notice. But there have been significant occasions in the past year where I have not received important emails (telling me something has been accepted for publication, for instance - calamity!), and also where my emails have not reached people at crucial times.
Ticking the Receipt Requested box on my email doesn't work. Most people I know ignore this. The only way to solve it is to ask the person, in my actual email, to send me back a quick Yes to say they received it. And hope they do.
Why am I rabbitting on about this? Simply because a number of US publishers have now decided that they will only respond to your submission if they are interested in reading more or offering publication. Zap!
Now that would be an entirely fair and reasonable way to go about dealing with the slush pile. Except ... how would you know if they received your submission in the first place? Delivery of snail mail or email is not 100% certain. By my calculations, not even 98% certain. It's a quandary indeed. All we writers can do is persevere, and hope Australia Post and the US Postal Service do the same.