Microsoft has stopped accepting new registrations for its free Custom Domains service, effective immediately. The move was announced today on the Windows Live Admin Center page, where users manage custom email addresses.

According to Mike Schackwitz, Principal Group Program Manager for the Outlook.com service, Microsoft will “wind down the Custom Domains product” while continuing to support existing custom email addresses “indefinitely.” The service has been in existence since 2005.

The move matches one that archrival Google made in December 2012, when it closed its Google Apps Free Edition. (That service had been in existence since 2006.) Today, Google Apps for Business costs $50 per user per year, with extra charges for enterprise features such as email archiving.

Microsoft’s goal is to move its customers to paid products, including the $60-a-year Office 365 Small Business (which includes Exchange Online, SharePoint Online, and Lync Online) and the $150-a-year Office 365 Small Business Premium (which adds a license to install the Office desktop programs and mobile apps for business use). All of the Office 365 business products include the ability to attach custom domains and create multiple aliases for a single address. (Office 365 Home Premium, a less expensive product, does not use Exchange Online nor does it support the addition of custom domains.)

According to a company spokesperson, existing customers will get a promotional offer:

Microsoft will offer existing Outlook.com custom domain customers a complimentary three month subscription to Office 365 Small Business Premium. Current customers using custom domains with Outlook.com will be notified via email in the coming weeks with further details and instructions.

The complimentary subscriptions will be available for up to five accounts and cannot be added to an existing Office 365 account.

I’ve written previously about using this service with several custom domains I own, and even wrote a tutorial on how to use the service to assign a custom domain to Microsoft’s free Outlook.com (formerly Hotmail) service. Based on reader email I received, a lot of you took advantage of that service for both personal use and small business domains.

Although the service no longer allows you to assign a new custom domain to Outlook.com, administrators of currently enrolled domains can continue to add and remove existing addresses for approximately two more months. On a yet-to-be-determined date in June (or perhaps July), administrators will lose the ability to create new addresses in the administrative control panel, and existing custom addresses will become standalone Outlook.com accounts, using the same custom address but managed individually by signing to the Outlook.com interface.

The move is disappointing, but not surprising. The fact that the Windows Live Admin Center continued to use the old Windows Live branding and was never updated with the modern design of Outlook.com was probably the biggest clue. In addition, the service has always been extremely limited, with administrators only able to add or delete addresses. And the relatively recent addition of a prominent Microsoft Office 365 link under the Sign In button was telling as well.

If you’re an existing Custom Domains customer, you should receive a notification of the change via email. If you have follow-up questions, use the contact form at the bottom of this post to send them my way via email.