Mechiel Lukkien 2f5d6069bf implement "requiretls", rfc 8689 ... with requiretls, the tls verification mode/rules for email deliveries can be changed by the sender/submitter. in two ways: 1. "requiretls" smtp extension to always enforce verified tls (with mta-sts or dnssec+dane), along the entire delivery path until delivery into the final destination mailbox (so entire transport is verified-tls-protected). 2. "tls-required: no" message header, to ignore any tls and tls verification errors even if the recipient domain has a policy that requires tls verification (mta-sts and/or dnssec+dane), allowing delivery of non-sensitive messages in case of misconfiguration/interoperability issues (at least useful for sending tls reports). we enable requiretls by default (only when tls is active), for smtp and submission. it can be disabled through the config. for each delivery attempt, we now store (per recipient domain, in the account of the sender) whether the smtp server supports starttls and requiretls. this support is shown (after having sent a first message) in the webmail when sending a message (the previous 3 bars under the address input field are now 5 bars, the first for starttls support, the last for requiretls support). when all recipient domains for a message are known to implement requiretls, requiretls is automatically selected for sending (instead of "default" tls behaviour). users can also select the "fallback to insecure" to add the "tls-required: no" header. new metrics are added for insight into requiretls errors and (some, not yet all) cases where tls-required-no ignored a tls/verification error. the admin can change the requiretls status for messages in the queue. so with default delivery attempts, when verified tls is required by failing, an admin could potentially change the field to "tls-required: no"-behaviour. messages received (over smtp) with the requiretls option, get a comment added to their Received header line, just before "id", after "with".		2023-10-24 10:10:46 +02:00
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dane.go	implement "requiretls", rfc 8689	2023-10-24 10:10:46 +02:00
dane_test.go	implement dnssec-awareness throughout code, and dane for incoming/outgoing mail delivery	2023-10-10 12:09:35 +02:00