I'm predicting that Google will end Gmail within the next five years. The company hasn't announced such a move -- nor would it.

But whether we like it or not, and whether even Google knows it or not, Gmail is doomed.

What is email, actually?

Email was created to serve as a "dumb pipe." In mobile network parlance, a "dumb pipe" is when a carrier exists to simply transfer bits to and from the user, without the ability to add services and applications or serve as a "smart" gatekeeper between what the user sees and doesn't see.

Carriers resist becoming "dumb pipes" because there's no money in it. A pipe is a faceless commodity, valued only by reliability and speed. In such a market, margins sink to zero or below zero, and it becomes a horrible business to be in.

"Dumb pipes" are exactly what users want. They want the carriers to provide fast, reliable, cheap mobile data connectivity. Then, they want to get their apps, services and social products from, you know, the Internet.

Email is the "dumb pipe" version of communication technology, which is why it remains popular. The idea behind email is that it's an unmediated communications medium. You send a message to someone. They get the message.

When people send you messages, they stack up in your in-box in reverse-chronological order, with the most recent ones on top.

Compare this with, say, Facebook, where you post a status update to your friends, and some tiny minority of them get it. Or, you send a message to someone on Facebook and the social network drops it into their "Other" folder, which hardly anyone ever checks.

Of course, email isn't entirely unmediated. Spammers ruined that. We rely on Google's "mediation" in determining what's spam and what isn't.

But still, at its core, email is by its very nature an unmediated communications medium, a "dumb pipe." And that's why people like email.

Why email is a problem for Google

You'll notice that Google has made repeated attempts to replace "dumb pipe" Gmail with something smarter. They tried Google Wave. That didn't work out.

They hoped people would use Google+ as a replacement for email. That didn't work, either.

They added prioritization. Then they added tabs, separating important messages from less important ones via separate containers labeled by default "Primary," "Promotions," "Social Messages," "Updates" and "Forums." That was vaguely popular with some users and ignored by others. Plus, it was a weak form of mediation -- merely reshuffling what's already there, but not inviting a fundamentally different way to use email.

This week, Google introduced an invitation-only service called Inbox. Another attempt by the company to mediate your dumb email pipe, Inbox is an alternative interface to your Gmail account, rather than something that requires starting over with a new account.

Instead of tabs, Inbox groups together and labels and color-codes messages according to categories.

One key feature of Inbox is that it performs searches based on the content of your messages and augments your inbox with that additional information. One way to look at this is that, instead of grabbing extraneous relevant data based on the contents of your Gmail messages and slotting it into Google Now, it shows you those Google Now cards immediately, right there in your in-box.

Inbox identifies addresses, phone numbers and items (such as purchases and flights) that have additional information on the other side of a link, then makes those links live so you can take quick action on them.

You can also do mailbox-like "snoozing" to have messages go away and return at some future time.

You can also "pin" messages so they stick around, rather than being buried in the in-box avalanche.

Inbox has many other features.

The bottom line is that it's a more radical mediation between the communication you have with other people and with the companies that provide goods, services and content to you.

The positive spin on this is that it brings way more power and intelligence to your email in-box.

The negative spin is that it takes something user-controlled, predictable, clear and linear and takes control away from the user, making email unpredictable, unclear and nonlinear.

That users will judge this and future mediated alternatives to email and label them either good or bad is irrelevant.

The fact is that Google, and companies like Google, hate unmediated anything.

The reason is that Google is in the algorithm business, using user-activity "signals" to customize and personalize the online experience and the ads that are served up as a result of those signals.

Google exists to mediate the unmediated. That's what it does.

That's what the company's search tool does: It mediates our relationship with the Internet.

That's why Google killed Google Reader, for example. Subscribing to an RSS feed and having an RSS reader deliver 100% of what the user signed up for in an orderly, linear and predictable and reliable fashion is a pointless business for Google.

It's also why I believe Google will kill Gmail as soon as it comes up with a mediated alternative everyone loves. Of course, Google may offer an antiquated "Gmail view" as a semi-obscure alternative to the default "Inbox"-like mediated experience.

But the bottom line is that dumb-pipe email is unmediated, and therefore it's a business that Google wants to get out of as soon as it can.

Say goodbye to the unmediated world of RSS, email and manual Web surfing. It was nice while it lasted. But there's just no money in it.