Similar to Sender_ID

Email authentication

Sender ID

Backscatter (email)

Bitmessage

Brand Indicators for Message Identification

DomainKeys Identified Mail

DMARC

POP before SMTP

S/MIME

Sender Policy Framework

DomainKeys

Bounce message

Forward-confirmed reverse DNS

Domain Name System blocklist

Google Panda

Google Penguin

Apache SpamAssassin

Instant messaging#Review of products

Authenticated Received Chain

Opt-in email

Keyword stuffing

Spamdexing