Microsoft’s experiment with getting customers to pay for additional features in Outlook will be priced at $3.99 per month, according to an updated page on Microsoft’s website, uncovered today. Earlier this year, news leaked of a new, paid version of Microsoft’s Outlook.com email service, called “Outlook Premium,” which would allow users to set up custom domain accounts to serve as more professional email addresses (rather than @outlook.com, @live.com or @hotmail.com). However, while Microsoft confirmed the pilot program at the time, it didn’t offer further details on launch, pricing, or full feature set.

Now we know more, thanks to a webpage spotted today by Thurrott.com, which details the pricing and features that will come with the subscription version of Outlook.

According to Outlook Premium’s landing page, users who choose to sign up for Outlook Premium will get five personalized email addresses, an ad-free inbox, and more, for $3.99 per month. However, the site notes that the entire first year will be free, with the subscription only kicking in afterward.

Of course, given that this is a pilot program, that price point could still be in flux. There is still no formal launch date for the service, which today requires that interested users request an invite to try out Outlook Premium, as opposed to being able to immediately sign up from the website.

While Microsoft has not yet made a formal announcement about its plans with Outlook Premium, it did earlier confirm that the program was considered an “experiment” in the pilot phases. The company said then it was not “an existing offering.”

The comment was made in response to a report from ZDNet, which uncovered the website for the pilot program, thanks to a reader’s tip. ZDNet also pointed out that the move could make sense as Microsoft had wound down support for custom domains in Outlook.com starting back in 2014. While existing users could continue use their personalized email addresses, Microsoft stopped accepting new registrations.

It’s possible that Microsoft felt there was enough demand for this feature that it could make sense as a premium add-on to Outlook.com.

What’s also interesting about Outlook Premium is that it will, to some extent, compete with Microsoft’s “Ad-Free Outlook,” priced at $19.95 per year – a bit less than Outlook Premium. Of course Premium offers more features. (See below).

According to an FAQ linked to from Outlook Premium’s website, Microsoft has partnered with domain provider GoDaddy to help Premium customers acquire the domain they want to use with their personalized email address. This domain will also be free for the first year, but then customers will need to renew the name every year with GoDaddy or another provider, if they choose to later transfer it.

During sign-up, Outlook Premium walks users through an interface where they can check for available domain names, and it will propose others. After completing this registration process, customers can then set their new personalized email as the default and choose which email they want to send from when composing a new message. Users are also able to share calendars, contacts and documents with the other people who have emails on the same domain.

In addition, Microsoft says that Outlook Premium will work with those customers who bought Office 365 Home with a personalized email address. By adding on the Premium service, users can invite up to four other individuals to create personalized emails on this account.

In other words, Premium works as both a standalone product and an add-on to Office 365 Home. This also means that Premium could work for both businesses and families who either want or need multiple email addresses that can be managed from the Outlook.com Premium Domain Dashboard.

Microsoft has been asked for comment on the status of this service, and we will update when one is provided.

Update: The company declined to comment further on the program, beyond providing the following statement:

“Outlook.com Premium is currently a small pilot program. We’re always investigating new features based on the wants and needs of our customers, and we have nothing more to share at this time.”

(hat-tip: Thurrott.com)