Lately I was receiving a lot of spam from a ‘.date’ TLD sources and wanted to block all these emails using Postfix.
Here is a solution found at:

Install the Postfix PCRE dictionary
apt-get install postfix-pcre
Configure postfix
postconf -e smtpd_sender_restrictions=pcre:/etc/postfix/rejected_domains
postconf -e reject_unauth_destinations=pcre:/etc/postfix/rejected_domains

Edit the new file /etc/postfix/rejected_domains with the following content:
/\.date$/ REJECT All Date Domains
Reload Postfix
service postfix reload