A threat actor is successfully sending email messages using a forged domain to a large variety of recipients. What can the domain owner do to help mitigate the problem?
a. Set a TXT record in its DNS.
b. Enable SPF on the MUAs of their employees.
c. Use a spam filter in its email system.
d. Use DKIM to generate private keys.
e. Use a strong hashing algorithm on the email headers.