The best way is to use Pando Software.
Founded in fall 2004 by Internet, e-commerce, digital music, and network security veterans, Pando Networks offer new tools for content delivery to the desktop.
Pando's underlying technology is a private and secure media delivery platform based on BitTorrent protocols.
The company's first product, Pando, is a free, intuitive consumer application that lets its users surpass e-mail attachment limits while using existing e-mail addresses.

Pando is free software that lets you send and receive files and folders of any size with your existing email address.

Features:
* Bypasses email attachment limits
* Opens .pando attachments emailed to you
* Accelerates downloads of huge files and folders

* Uses your existing email address
* Drag, drop and send entire folders
* Sends small .pando attachments, never clogs inboxes
* Easy: No web uploads or compression, just send via email!

It's 100% Clean. No spyware, no adware.

You cand download Pando from here.

There is also a Pando Plug-In for Yahoo! Messenger

You can download it from here.
Instructions here.