SSL/TLS vs plaintext/STARTTLS port numbersĭepending on the type of connection and what encryption is supported, different port numbers might be needed. Adding proper encryption to these without breaking existing behaviour was a significant challenge. SSL/TLS and STARTTLS had not been invented yet when IMAP, POP, and SMTP were already well established. To understand SSL/TLS and STARTTLS, it's necessary to understand the history behind these standards and how the industry has evolved to deal with existing user and client behaviors and new threats.
#Zimbra desktop prevent forwarding upgrade#
"TLS, if available" meant that the program would try to use STARTTLS to upgrade the connection if the server supported this, but otherwise use an insecure connection. These versions also used the term "TLS, if available". Older versions of Thunderbird in particular used "TLS" to mean that STARTTLS should be used to upgrade the connection, and the connection should fail if STARTTLS is not supported.
#Zimbra desktop prevent forwarding software#
One cause of confusion around the names of these different technologies is that some email software incorrectly uses the term TLS when they should have used STARTTLS. Current software supports TLS v1.0, TLS v1.1, and TLS v1.2, and many sites and services now strongly recommend at least TLS v1.2 for its overall improved security profile. SSL has been officially deprecated (as of May 2018) and is no longer in use by modern online services. While almost all online services support SSL/TLS today, not all services support the newest TLS v1.3. This might mean that if the server supports the newest TLS v1.3, but the email client connecting to the server only supports TLS v1.1, both sides might use TLS v1.1. When a connection is made to a port that has SSL or TLS, or when an insecure connection is upgraded to secure by STARTTLS, both sides of the connection will agree on a particular version depending on what is supported. The version numbers of SSL and TLS in order from oldest to newest is: STARTTLS helped to reduce this risk by taking an existing insecure connection and upgrading it to a secure connection that used SSL/TLS. This put personal information in danger of being stolen. Before encryption was standard, many connections between an email client and the server were done insecurely. The terms SSL and TLS are often switched and used interchangeably. It is supported by all modern and secure systems that handle internet traffic, including Fastmail. This prevents any third parties from spying on these communications. SSL and TLS are the standard technology to encrypt connections between two computers. There's often quite a bit of confusion around the different terms SSL, TLS, and STARTTLS. If you are looking for information on setting up your email client, please go here. This is an informational page about the history of SSL, TLS, and STARTTLS and the differences between these protocols.
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