Microsoft is planning to introduce a dark mode to its Outlook.com web mail service. While the software giant introduced a temporary dark mode for Halloween last year, Microsoft has been working on a new dark mode for Outlook.com for the past few months. Microsoft has started teasing that the new dark mode will be available soon.

“One reason for the delay is our insistence that we deliver the best Dark Mode of any leading email client (you’ll understand when you see it, I guarantee),” explains an Outlook.com team member in a feedback post. “The sneak preview you saw last year at Halloween was a prototype that required a lot more work to be ready for prime time.” Microsoft says it has redesigned the colors and code “multiple times,” and it’s in the final stretch of introducing the new theme in Outlook.com.

The https://t.co/0b8YLi7Qx0 Halloween theme is quite something pic.twitter.com/JIMc3ZSlPS — Tom Warren (@tomwarren) October 27, 2017

A dark mode for Outlook.com is one of the most highly requested features for Microsoft’s web mail service, according to listings on the Outlook.com feedback site. Microsoft first introduced Outlook.com nearly six years ago as a replacement for its aging Hotmail web service, and it now has around 400 million active users. Microsoft has been tweaking its web mail service ever since with updated features, and a new design started rolling out back in March.