The black theme has been around in Outlook for Windows for some time. However, unlike Outlook Web App, or, Microsoft Teams, the black theme was not a true dark mode. Some aspects of the black theme were still fully illuminated, such as when you read or composed a message.
The screenshot below is an example of how the black theme changes certain aspects such as the folder view and toolbars to black but leaves the email preview pane in white.
Similarly, when you compose an email the message body is also in white.
The new Black Theme for Outlook
Starting with version 1907 for Office Insiders, the Outlook team has extended the black theme so it now incorporates the message body and the composition panes.
Note: Anyone can enroll in the Office Insider program. However, Office Insiders receive weekly updates, which could be subject to bugs.
UPDATE 10-5-19: For those on the Monthly Channel, you can get dark mode with the 1909 monthly channel update (released September 30th).
With version 1907 the message preview pane defaults to black.
Similarly, when you compose an email the message body is now black.
Turning the lights on
It is also possible to turn the lights on for both the message preview and composition screens. This can be useful if an email is not rendering properly in the black theme, or, you simply need to make the message brighter.
To do this in message preview, click the Switch Background button. The icon is represented as the sun.
The message preview will turn to white and the Switch Background button will now be represented as a moon. To turn the lights back off, click the Switch Background button again, which is currently represented as a moon.
The Switch Background button is also available when you are composing an email message. Simply click the Switch Background button to switch the email composition pane between light and dark mode.
Always keep the lights on
If you prefer the old behavior (prior to 1907) where the lights were always on for the reading pane, this option is still available.
Click on the File menu and select Options. From the Outlook Options dialog, select the General tab and check the box Never change the message background color. Click Ok to save your changes. When you select your next email message, and each message thereafter, the lights will remain on.
To revert this change, simply uncheck the previously selected box.
How to switch to the black theme (dark mode) in Outlook
To switch to the black theme in Outlook (and by extension, the entire Office suite), click the File menu and select Office Account.
Under the section Office Theme, pick Black from the drop-down.
You will be immediately switched to the black theme (dark mode).
So, what do you think about the updated black theme? Drop a comment below or join the conversation on Twitter @SuperTekBoy.