Similar to Bitmessage

S/MIME

Jami (software)

Proton VPN

Riseup

Signal Protocol

Tuta (email)

ZeroNet

Signal (software)

Shadowsocks

Proton Mail

Email authentication

Brand Indicators for Message Identification

DomainKeys Identified Mail

DMARC

POP before SMTP

Sender ID

Sender Policy Framework

DomainKeys

Bounce message

Backscatter (email)

Forward-confirmed reverse DNS

Encryption software