One of my favorite features in Outlook.com is the ability to add a POP3 mail address to send from. I use my domain mail a lot, and even though I could use custom domains to manage my mail, I have decided to keep my original Outlook.com address.
You can now send through your domain provider’s servers, meaning you get the annoying “Sent on behalf of” in the email header. So, I set up my domain mail as my default mail address, and it turns out that Outlook.com will always use this, even though you use Outlook.com on your Windows Phone. When I open the mail app, which is associated with my Outlook.com address, it will actually send from firstname.lastname@example.org, which is a really nice detail.