Which DNS resource record can indicate how long any "DNS poisoning" could last?

Craig received a report of all the computers on the network that showed all the missing patches and weak passwords. What type of software generated this report?

Bob, your senior colleague, has sent you a mail regarding aa deal with one of the clients.
You are requested to accept the offer and you oblige.
After 2 days, Bob denies that he had ever sent a mail.
What do you want to "know" to prove yourself that it was Bob who had send a mail?

You have compromised a server on a network and successfully opened a shell. You aimed to identify all operating systems running on the network. However, as you attempt to fingerprint all machines in the network using the nmap syntax below, it is not going through.

What seems to be wrong?

Which one of the following Google advanced search operators allows an attacker to restrict the results to
those websites in the given domain?