Select Multiple

Bulk selection has not been removed; in Outlook.com, restore the selection boxes under Settings → Mail → Layout, or enter selection mode from a sender’s icon.

Restore the checkboxes

1. Open Outlook.com and select the Settings gear.
2. Select Mail → Layout. Microsoft documents this as the location for message-list display settings.^1^
3. Find How do you want messages to appear in the message list?
4. Select Checkboxes instead of Sender images or Name only.
5. Close Settings. Checkboxes should appear beside the messages, allowing you to select several and then choose Delete.^2^

If your account does not yet show that setting, hover over the sender’s picture or initials beside a message. When it changes to a checkbox, select it; Outlook should enter selection mode and display checkboxes for the remaining messages.^2^

You can also look for the square Select icon at the right of the folder name above the message list.^3^

On a phone or mobile browser

Press and hold a message—or tap its circular sender icon—then tap the other messages. Use the trash icon to delete them, or open the three-dot menu for Select All.^4^

Be careful with Select All or Empty folder: deleting selected messages moves them to Deleted Items, while subsequently emptying recovery locations can make deletion permanent.^5^

References

1. Change the look of your mailbox in Outlook.com and Outlook on the web
2. Where are the SELECTION BOXES on Outlook? Why are they NOW GONE??? - Microsoft Q&A
3. Check boxes have disappeared - Microsoft Q&A
4. How do I select multiple emails? | Microsoft Support
5. Delete email in Outlook.com | Microsoft Support