I routinely have correspondences where the other person will simply stop returning messages--including business correspondences. There's always the notion that a phone or computer didn't receive the message, but when it happens on multiple occasions, it seems rude and counter productive.
I'm seldom to the point where a written exchange bores or annoys me into not responding, especially when the written exchange involves business matters. Yet, I find that many people will do this with me and with others.
I don't think I'm some kind of idealistic returns-all-messages wonder-boy who goes against the grain in being extra polite with anything, but is there some unwritten code that dictates when an exchange can be cut off?
As a new form of communication, the mores for email are unclear.
I have read if you don't receive a response in a week, send a tickler message. Sometimes things do end up in spam folders when they're not supposed to. And I had repeated problems with email from my wedding caterer, which, yes, did make her appear unprofessional to me, the customer. I noticed she used an obscure email host/provider/whatever it's called.
In my profession, I have read that the standard for a response to a client is a business day. Most try to respond faster.
If a "business" exchange can be boring or annoying, you're doing it wrong. Email is a poor medium for actual discussion. It's good for straight-forward questions, setting appointments, giving straight-forward assignments, and providing information that needs no or minimal response. If you want significant back-and-forth on the prudence of investing in cheddar futures, pick up the phone or arrange a meeting.
An open-ended discussion can be cut-off at any point, because it shouldn't have been begun via email in the first place. I don't think it's necessary to confirm receipt of an email unless there have been problems with email correspondence, confirmation is requested, or the email contains complicated or extensive instructions or information, in which case a confirmation request may be implied. Appointments set by email should be confirmed with different language, but the same sense, as confirmation of a formal social invitation - repeating the date, time, and location. For phone calls, make sure it's clear who's initiating the call.
With spam filters and such the person may honestly not be getting the email. Switch to calling with and email followup to the call. Even if the person does not get them you have a paper trail.
The other option when you need answers is to setup the email such as we are doing x unless you email otherwise.
Its always been an option. That's the joy of e-mail. You can contact me at all hours of the day ... and I can get around to it if, and when, I feel like it.
Are you wasting time with very lengthy e-mails? If so, expect to be ignored.
Example: I work in RE Development/Invesment. An architect contacted me via e-mail yesterday looking for work. The only relevant information in the whole thing was withheld until the end. I care about what he has to offer me, and that was the last thing that appeared in his message. He was deleted.
To give you more specific advice on your situation, I would have to better know your circumstances.
I'm not sure if you care for the opinion of a 16 year old or not, but for my social circle it's rude to not reply at all to important matters that require a reply. Aside from that, it isn't rude to not reply (although in informal, freindly texting it can be). I don't know why that's the way it is for us, it just is.