Anti-spam techniques

The U.S. Department of Energy Computer Incident Advisory Capability (CIAC) has provided specific countermeasures against electronic mail spamming.

Some popular methods for filtering and refusing spam include e-mail filtering based on the content of the e-mail, DNS-based blackhole lists (DNSBL), greylisting, spamtraps, Enforcing technical requirements of e-mail (SMTP), checksumming systems to detect bulk email, and by putting some sort of cost on the sender via a Proof-of-work system or a micropayment. Each method has strengths and weaknesses and each is controversial due to its weaknesses.