STARTTLS vs SSL/TLS

ssl smtp starttls
paweloque picture paweloque · Apr 4, 2011 · Viewed 49.9k times · Source

Mailclients offer both settings, the STARTTLS and SSL/TLS. What is the difference between STARTTLS and SSL/TLS?

Answer

james.garriss picture james.garriss · Jan 18, 2013

The clearest explanation that I've read is from FastMail:

SSL and TLS both provide a way to encrypt a communication channel between two computers (e.g. your computer and our server). TLS is the successor to SSL and the terms SSL and TLS are used interchangeably unless you're referring to a specific version of the protocol.

STARTTLS is a way to take an existing insecure connection, and upgrade it to a secure connection using SSL/TLS. Note that despite having TLS in the name, STARTTLS doesn't mean you have to use TLS, you can use SSL.

Read the rest of the info they have, including a discussion of port numbers and POP/IMAP vs SMTP, here: https://www.fastmail.fm/help/technology_ssl_vs_tls_starttls.html

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