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Email

What is SMTP Relay?

A server that forwards email on behalf of the sender, which can either protect the sender's identity or be exploited for spam and spoofing.

SMTP relays are intermediate servers that pass email between the sender and recipient's mail servers.

Privacy Aspects

  • Open relays: Historically exploited for anonymous spam (now mostly blocked)
  • Authenticated relays: Services like SendGrid, Mailgun provide email sending without revealing your server's IP
  • Tor email: Services like OnionMail relay email through Tor

Header Privacy

  • Each relay adds a "Received" header, creating a traceable path
  • Some privacy-focused providers strip identifying headers
  • Using a relay adds a hop between you and the recipient, partially anonymizing the origin

For Privacy

  • Use a privacy-focused email provider that strips identifying headers
  • Consider that email is inherently not private — use encrypted messaging for sensitive communications
  • If you must use email, encrypt with PGP and understand that metadata is still visible

Related Terms

Email Header Analysis

Examining the metadata in email headers to trace the path of a message, identify the true sender, and detect spoofing attempts.

S/MIME

A standard for public key encryption and signing of email messages, supported natively by most email clients.

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