Extracting domain names from email addresses with the help of regular expressions takes just a nanosecond once you have the formula. The formula is the key.
Some things never change. Love it or hate it, but everyone still needs email.
Anti-Spam Defense: Using Postfix With smtpd Access Restrictions
Fighting spam, aren’t we all… To stem the tide of unwanted junk mail look no further than the built-in access restrictions in Postfix.