Hi Winter,
What's your account type? Exchange, POP or IMAP?
Can you find these emails on the web mail?
Check if emails are moved to Deleted Item folder? If yes, move them back to the original folder.
Sometimes, emails become invisible due to view settings instead of getting deleted. Try searching in "All Mailbox" scope to see if you can find these emails.
If they are not deleted, we can reset view in case a filter was applied. Click View tab > Reset View.
Any updates, please feel free to post back.
Regards,
Perry
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