Hi @Lewis Smith
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For a better study, please provide more details about this case:
Has this problem persisted?
After deleting messages, do deleted emails reappear after being deleted from the Deleted Items folder?
According to my tests, when a message is deleted from the message preview pane, it automatically jumps to the next message. However, if this message opens a new window, the message in the new window is not deleted.
Additionally, there may be a known issue after updating to version 2412 (Build 18324.20168). Classic Outlook may crash when starting a new email, or when replying or forwarding an email. Please try the fixes in the article: Classic Outlook crashes on reply and forward - Microsoft Support
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