Check the missing emails from outlook are appeared in other mail clients (owa, mobile etc.). If so, try recreating the profile in outlook and check the missing mails are back
all mail disapear

Hi dear expert
after install kb5001779 all inbox,sent and... mail in some user mailbox disappear
please give me hand to fix issue
Tank you in advance
2 answers
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KyleXu-MSFT 25,746 Reputation points
2021-04-19T06:02:26.143+00:00 First, there doesn't exist any feedback about that this KB will cause email missing. It isn't an issue that caused by this Security Update,
Use command below to check whether there exist emails in this mailbox Inbox and Sent Items:
Get-MailboxFolderStatistics User1 | ft Identity,FolderAndSubfolderSize
If emails exist in this mailbox, you can try to check from OWA or create a new profile. You can also use New-MailboxExportRequest to export emails from this mailbox.
If there real doesn't exist emails in this mailbox inbox, try to check whether there exist emails in "Deletions" or "Purges", if there exist emails in those folders, it means those email was delete by mistake. You can follow this picture below to recover those emails:
If there doesn't exist emails in those folders, you will cannot find and recover those emails.
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