...but wait!!! There is an easier way to do your mail

On Windows, at least, it is much easier and more convenient to interact with an e-mail client native to the machine and OS you're working on.

Cut, Copy, Paste between your e-mail client and other programs are instantaneous, as are filters, searches and comparisons.

The big Windows e-mail clients such as Outlook also integrate with Microsoft Office and is both an ActiveX/COM server and client, so that you can integrate it with custom developed applications.

That said:

It is becoming increasingly irrelevant to keep your data (all of it!) on your local machine, and within the next 5 years I suspect that the practice would've all but disappeared, except for specialist applications.

In fact, that applies not only to data, but to the applications themselves, both of which would've migrated into some cloud environment.

What I am seeing is that what today is your PC/Server/LAN would've moved into a virtual equivalent in the cloud, and that your current device of interacting with your data (PC) will be replaced by a device providing merely a window into your virtual environment. This can be a low spec PC, iPhone, Smart Phone, Android device, whatever, all giving you the same user interface to your system. That means that your information system becomes independent of the device you are using - you can access it anywhere in the world, anytime, from any device.

(In a way, we are back to the days of the huge monolithic mainframes, with terminals connected to it.)

Anyway, in this environment it again makes sense to implement a dedicated e-mail client, since your data stays in the cloud anyway, and the dedicated e-mail client provides the speed and ease of use which it is designed for.

In South Africa the current problem to this is the currently still prohibitive cost of high speed broadband internet.

And, of course, being offline is not something that can still be an option.