How to block (whitelist / blacklist) an email address

Google calls this an Email allowlist and Email denylist.

Do to this, head to the relevant Google domain.

Navigate to:

Apps > Google Workspace > Gmail > Routing

At the very bottom of the Routing page you should find the option to Manage address lists.

NOTE:

I have here under the SPAM_Email list added the address: *@nifty.com

However, since doing this Tom has still received spam/phishing email from this domain (a known Chinese phishing website). Unsure if they are spoofing their address/domain and thus spam still gets through, so I have also tried the below method for blocking this domain:

Apps > Google Workspace > Gmail > Spam, Phishing and Malware

Under Blocked senders I have added a rule for *@nifty.com (copying a previous rule by Ekco: M2MG00003301 - rsb45788@nifty.com).