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WttW: Can you STARTTLS?
Word to the Wise just posted another insightful article:
Email supports TLS (Transport Layer Security), what we used to call SSL. Unlike the web, which split it’s TLS support off into a completely different protocol – https, listening on port 443 vs http listening on port 80 – SMTP implements it inside it’s non-encrypted protocol. A mailserver advertises that it supports this by having the word “STARTTLS” in the banner it sends after you connect to it. Before you do much else you send the command “STARTTLS”. At this point the tcp connection to the mailserver stops speaking SMTP and is ready for the complex binary dance that is a TLS handshake. Once the negotiation of protocols and ciphers and session tokens is done SMTP comes back. It looks just like it did before, but now it’s all being tunneled over a secure, encrypted TLS session. Sometimes you want to find out a few more details about how a
Continued here: Can you STARTTLS?
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