I wanted to know if there is a way to set a rule on admin center to be informed how many people have received an email from a sender, it can help me to detect some phishing emails that have not been detected by protection rules.
Well, any sort or rule will not apply retroactively, as in it will not flag any messages that were already received. Use the Search-Mailbox cmdlet to locate such messages, or perform an eDiscovery search.
