Microsoft is introducing the ability to multiple Outlook inboxes

Microsoft will add the ability to search across multiple accounts simultaneously in Outlook for the web, with results combined into one ranked list. The feature will appear for users starting next month, and standard email actions will be available from search results.

• Search to cover multiple mailboxes at once
• Results combined into one ranked list
• Delete, reply and forward available from results
• Feature coming to Outlook for web next month