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> 2004: First attempt to authenticate Internet mail senders initiated This is the most insane part to me.

• Avamander 4y ago
  Not mentioned in that PDF - MTA-STS was finalized in 2018, finally making proper TLS between MTAs possible. There's still no MUA-STS, which would actually be the email-equivalent of HSTS.
  • hericium 4y ago
    > There's still no MUA-STS, which would actually be the email-equivalent of HSTS. MUAs can choose to respect TLSA record if one exists for the service its using (submission(s), IMAP/POP3). MTAs could also resolve "25._tcp" TLSa records but, as you mentioned, there are more suiting mechanisms.
    • Avamander 4y ago
      I'm not sure attaching additional semantics to existing TLSA records would be a great idea.
      • teddyh 4y ago
        What other semantics could a TLSA record on a _25._tcp subdomain possibly have?
        • Avamander 4y ago
          Its original semantics as designed. Attaching MUA-STS, MTA-STS or HSTS to existing TLSA records would mean changing the records' meaning, that's not okay.