Page 134 of the DSE Networks & Infrastructure knowledge center, with source-backed guidance and practical next steps.
Guidance for resilient networks, Wi-Fi, firewalls, cabling, power, exposure reduction, and connected-device planning.
A DNSSEC-secure TLSA RRset with at least one usable record requires both TLS encryption and SMTP server authentication. If all records in a secure nonempty TLSA RRset are unusable, TLS remains mandatory but authentication is not; lookup errors defer delivery or try another MX.
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Sieve tests are arguments to conditional commands and select which action block executes for a message. The base language supports keep, fileinto, redirect, and discard, while implementations may bound action counts and restrict incompatible combinations.
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Encoded-words are allowed only in specified text fields, comments, and phrase words; they are forbidden in addr-specs, quoted strings, Received fields, and MIME parameters.
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A mail client uses the domain part of the user’s address to query service-specific SRV names and obtains the selected endpoint’s target host and port.
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A delivery-status notification is a multipart/report with report-type delivery-status, a human-readable part, and a message/delivery-status part; returned original content is optional.
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A sender discovers MTA-STS through the policy domain’s _mta-sts TXT record, whose id value distinguishes policy revisions. In enforce mode, the sender requires STARTTLS and valid MX identity for each candidate, while a still-valid cached policy remains applicable when live retrieval fails.
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Content-Disposition says whether a MIME body part is intended for automatic inline presentation or for user-initiated attachment handling; it does not define the media format.
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A Mailbox is a named collection of Email objects, and moving an Email between Mailboxes does not change the Email object’s identifier. An Email object represents one RFC 5322 message independently of the Mailbox and Thread objects that organize or group it.
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After a 220 response to STARTTLS, the client begins the TLS handshake before sending any further SMTP command. A successful TLS handshake resets SMTP to its initial state; both peers discard pre-TLS protocol knowledge and the client sends a new EHLO.
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An SMTP server advertising SMTPUTF8 accepts UTF-8 wherever the SMTP mailbox grammar permits a mailbox value. A client may send internationalized mailbox names and UTF-8 headers only after the server advertises SMTPUTF8 in its EHLO response.
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