Sending, receiving, and organizing email in Outlook.com
I can understand how alarming it must be to see several hundred emails suddenly disappear while you were carefully deleting only a few messages at a time. You did the right thing by stopping further deletions or bulk actions, as this helps avoid making the situation more difficult to investigate.
Since the Deleted Items folder contains only the 158 messages you intentionally removed, the other messages may have been moved, hidden by the current view, or placed in the recoverable-items area rather than deleted permanently.
Please first open Outlook.com in a desktop browser and go to Deleted Items > Recover items deleted from this folder. If the missing messages appear there, restore a small number first and confirm where they return before restoring the rest.
If they are not listed, search for one specific missing message using its sender, subject, or approximate date, and set the search scope to All folders. This can help determine whether the message was moved to another folder or excluded from the current Inbox view.
If neither the search nor the recoverable-items area finds the messages, I understand this may be especially worrying given how many emails are involved. Please contact Outlook.com Support by selecting Help > Help in Outlook.com, describing the issue, and choosing Still need help? > Yes when that option appears. Include the approximate time the Inbox count dropped to nine, the Z-to-A sorting order, and the fact that Shift was used to select small groups of messages.
Please note that this is a user-to-user support forum. Contributors cannot access mailbox activity logs or restore messages from Microsoft’s systems, so Outlook.com Support is the appropriate team to investigate whether recovery is still possible. Until the mailbox has been reviewed, avoid using Sweep, changing rules, emptying folders, or performing additional bulk deletions. Thank you so much for your understanding.
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