While the switch is off, the answers that tell a mail app where to connect
stop offering what the switch closed, so a new phone or desktop app is not
sent to a port that is shut or a sign-in that will be refused:
- Thunderbird-style autoconfig (/mail/config-v1.1.xml and its other
paths) and Outlook autodiscover leave out IMAP, POP3 and SMTP
submission.
- PACC (/.well-known/user-agent-configuration.json) offers JMAP, CalDAV,
CardDAV and WebDAV, and no IMAP, POP3, SMTP or ManageSieve. The document
is rendered once per configuration load, so the JMAP-only version is
rendered beside it and chosen per request; the _ua-auto-config digest in
the suggested zone follows, since it hashes the same document.
- The suggested zone publishes _imap, _imaps, _pop3, _pop3s, _submission
and _submissions with target "." -- "not offered", RFC 6186 section 3.4 --
the spec's decision, rather than dropping them: a client that looks is
told, and an automatically managed zone replaces the old records instead
of leaving them behind.
- It also drops the TLSA records for ports 993 and 995. A TLS pin for a
port the switch has closed advertises a service that is not there.
Submission's 465 keeps its record: the SMTP lock keeps that port open.
The switch is read per answer, as sign-in reads it, so every node agrees
the moment it turns. Inbound mail, MX records and the JMAP, CalDAV and
CardDAV answers are untouched.
tests/e2e/legacy_protocols.py checks all four on a running server: with the
switch on they offer IMAP, POP3 and SMTP (the control); while it is off
they offer none of them and every legacy SRV name has target "."; and once
it is back on, autoconfig and the zone read as they did before. All checks
pass.
jcoffey-dev
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