Microsoft has began rolling out a feature that will enable Windows Live Hotmail users to send and receive email from other existing email addresses while using Hotmail. This essentially turns Hotmail into a web based email client.
In the Hotmail Options menu under the heading "Sending/Receiving email from other accounts," users can add their other webmail addresses, and then use Hotmail to send and receive messages.
“Implementing this was fairly straightforward given the architecture of Hotmail, our POP aggregation support, and the "Send As" feature that lets you send mail from any validated email address. We just needed to tweak the way we store and look up email addresses, build the first-run experience, and we had it,” Microsoft wrote in a blog post.
For a long time, Hotmail users has had the ability to create a Hotmail address, sign in, and aggregate mail from other services over POP. Nothing has changed about that feature.
The key change here is that you don't have to create a new address to try Hotmail. If you've already got an address from any other email service, you can now use that to sign into Hotmail. And, when you set up POP aggregation from that other email service, you now can use Hotmail essentially as a client.
Of course, Gmail had this feature for long – Hotmail is just playing catch-up.