I have confused for many time about these three terms, STARTTLS vs SSL vs TLS.

Therefore, I did some research and summarize them in short.

  • STARTTLS is a way to use an existing insecure connection and upgrade it to be secured through TLS or SSL.
  • SSL/TLS is a way to form secure connection natively.
  • TLS is the successor to SSL. Their history is SSLv2 -> SSLv3 -> TLSv1.0 -> TLSv1.1 -> TLSv1.2
  • SMTP SSL/TLS encrypted over port 465
  • SMTP with STARTTLS upgrading over port 587 (ISP can block port 25 to prevent most of the spammer in ISP network)

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