Microsoft continues to update its Outlook.com service, and as well as the recently launched IMAP support, they have now borrowed a page out of Google's book and also added + aliases support for email, a feature discovered by Rafael Rivera of Within Windows.
For example, email@example.com will land in my firstname.lastname@example.org inbox and allow me to filter email coming in off neobond+junk, which I could use to enter competitions or as a throw away address that I can filter directly to a folder or delete. Any and multiple combinations work after the + (as long as it's well formed) and lands in your primary email folder if you haven't set up any rules for the alias.
This feature also works with custom domain names used with Outlook, and the same feature can also be used on Gmail. This is not to be confused with an actual alias, which can also be setup through the Outlook.com's More mail settings page; aliases allow in and outbound mailing, while the + aliases are inbound only. In any case, it's a pretty cool feature that could be useful.
Source: Within Windows