Microsoft has started rolling out a Classic Outlook theme for users of Outlook on the web and the New Outlook for Windows.
This new Outlook theme is rolling out as part of a targeted release beginning mid-August and expected to complete by the end of September. The theme will become generally available worldwide between late September and late October.
"When enabled, the setting applies coordinated changes across the Outlook experience, including visual styling, layout, typography, icons, and selected interactions," Microsoft said in a Microsoft 365 Message Center update.