Lerner’s “inbox” is a file in a directory. It contains email from all senders, both internal and external. Likewise for the “sent” e-mail, it is a file in a directory and it contains email sent to all recipients, both internal and external.
A disk failure corrupting the inbox file is not going to selectively destroy only email from external senders.
A disk failure corrupting the sent file is not going to selectively destroy only email sent to external recipients.
A disk failure corrupting so precisely BOTH these files.... is a Mount Everest of BS.