Outlook.com discontinued custom domain support
If you are using Outlook.com as an email service for your custom domain, you will not be able to add or remove accounts in the future. You should receive a notification from them as well. Outlook.com discontinued custom domain support and you will only be able to manage your existing email accounts. In future, you will not be able to add or removes email accounts.
You can still manage your existing email accounts via login to Outlook.com account. Following is their official update on http://domains.live.com/ URL:
Changes to custom domains with Outlook.com
Outlook.com no longer offers support for new custom domain sign ups. New customers looking to manage custom domains are encouraged to use Office 365, Microsoft’s premium online service, which also includes enterprise-class mail, collaboration and communication tools.
If you currently use custom domains with Outlook.com
We will continue to support the ability to log in to Outlook.com with your existing custom domain email address, but in the future, you will no longer be able to add or remove accounts in your domain.
For domain administrators who wish to continue to manage email addresses in their domain, we will be providing the option to migrate your account to Office 365. As part of Office 365, you will be able to continue managing your custom domains, as well as use many additional productivity tools including shared calendars, cloud storage and instant messaging.
Current customers using custom domains with Outlook.com will be notified via email in the coming weeks with further details and instructions on how to migrate.