A. Search the sender's email address by using Email Log Search. Identify the users that received the messages. Instruct them to mark them as spam in Gmail, delete the messages, and empty the trash.

B. Search for the sender's email address by using the security investigation tool. Mark the messages as phishing. Add the sender's email address to the Blocked senders list in the Spam, Phishing and Malware setting in Gmail to automatically reject future messages.

C. Collect a list of users who received the messages. Search the recipients' email addresses in Google Vault. Export and download the malicious emails in PST file format. Add the sender's email address to a quarantine list setting in Gmail to quarantine any future emails from the sender.

D. Search for the sender's email address by using the security investigation tool. Delete the messages.Turn on the safety options for spoofing and authentication protection in Gmail settings.