# Discover mail endpoints through service-specific SRV records > Use RFC 6186 — Use of SRV Records for Locating Email Submission/Access Services to review this narrow operational decision without extending the source beyond its stated scope. - Canonical URL: https://update.dsesecurity.com/updates/discover-mail-endpoints-through-service-specific-srv-records/ - Publisher: Detection Systems & Engineering (DSE Security) - Author: DSE Security Editorial Team - Published: 2026-08-27T12:17:04+00:00 - Modified: 2026-08-27T12:36:15+00:00 - Last reviewed by DSE: 2026-08-26 - Resource type: Checklist - DSE priority: Advisory - Topics: Cybersecurity, Networks & Infrastructure - Reading time: 3 minutes ## What you need to know Use RFC 6186 — Use of SRV Records for Locating Email Submission/Access Services to review this narrow operational decision without extending the source beyond its stated scope. ## Potentially affected Teams, systems, services, or facilities within the stated scope of RFC 6186 — Use of SRV Records for Locating Email Submission/Access Services ## DSE recommendation Compare the observed state with the cited official source, document applicability and exceptions, and test any approved change with rollback safeguards. ## Article Treat this document as a focused evidence review: Discover mail endpoints through service-specific SRV records. Only the official source and traced locations below supply facts. Confirm applicability before acting. ## Source fact: The official [RFC 6186 — Use of SRV Records for Locating Email Submission/Access Services](https://www.rfc-editor.org/rfc/rfc6186.html) from RFC Editor / Internet Engineering Task Force supports the following bounded statements: - 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. The research record locates this support at Section 4 (Guidance for MUAs). - The _imap and _pop3 labels identify explicit-TLS-upgrade services, while _imaps and _pop3s identify services that begin TLS immediately on connection. The research record locates this support at Sections 3.2 (IMAP) and 3.3 (POP3). - When several SRV records describe one service, the client must apply SRV priority and weight; a target of a single dot marks that service unavailable. The research record locates this support at Sections 3.4 (Priority for Domain Preferences) and 4 (Guidance for MUAs). Keep the evidence boundary at these traced claims. They support a review of sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling; they do not support conclusions outside the source’s stated conditions. ## What the source does not establish This RFC evidence supports only the named mail-protocol decision; it does not prove provider support, deliverability, or compliance for a particular flow. The citation is not a substitute for observed state, authorization, compliance evidence, or dependency health. Examine authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers before translating the source into an operational decision. ## Applicability questions - For source statement 1 at Section 4 (Guidance for MUAs), which observable configuration, record, or test can confirm applicability here? - For source statement 2 at Sections 3.2 (IMAP) and 3.3 (POP3), which observable configuration, record, or test can confirm applicability here? - For source statement 3 at Sections 3.4 (Priority for Domain Preferences) and 4 (Guidance for MUAs), which observable configuration, record, or test can confirm applicability here? - Within sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling, which versions, roles, and configuration states define the review population? - Could authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers invalidate the test, hide a failure, or change applicability? - Who owns the decision, and which observation requires stopping, escalation, or rollback? ## DSE recommendation: DSE recommends using the cited source as the evidence anchor for this decision. Anchor the review in the cited section and keep observation separate from interpretation. Record the source location, examined part of sending domains, receiving domains, message agents, headers, authentication results, policy records, and failure handling, observed and expected states, owner, and reason for deviation. An implementation decision needs an owner, approved window, prechecks, observable outcome, stop authority, and rollback path. Validate authoritative DNS, certificates, time, gateways, identity stores, reputation services, and third-party mail providers before and after the test, and store only sanitized operational evidence. ## Verification and evidence Keep the source locations Section 4 (Guidance for MUAs); Sections 3.2 (IMAP) and 3.3 (POP3); Sections 3.4 (Priority for Domain Preferences) and 4 (Guidance for MUAs) adjacent to the sanitized artifacts used for comparison. Prefer sanitized messages, DNS records, SMTP transcripts, authentication results, policy evaluation, and delivery or rejection logs, with enough identity and timing data for an independent recheck. Keep before-state evidence, approval, test or change result, exceptions, and after-state evidence together. Use an approved lab, window, or nonproduction path for risky tests. Set a recheck trigger for version, architecture, dependency, vendor, incident, or ownership change. A check proves only what was observed. ## Official references - [RFC 6186 — Use of SRV Records for Locating Email Submission/Access Services](https://www.rfc-editor.org/rfc/rfc6186.html) — RFC Editor / Internet Engineering Task Force ## Primary reference - Name: RFC 6186 — Use of SRV Records for Locating Email Submission/Access Services - Authority: www.rfc-editor.org - URL: https://www.rfc-editor.org/rfc/rfc6186.html - Source publication date: Not stated by the source ## Citation and use Preferred citation: “Discover mail endpoints through service-specific SRV records,” DSE Security, https://update.dsesecurity.com/updates/discover-mail-endpoints-through-service-specific-srv-records/ Publishing principles: https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/ Usage and citation policy: https://update.dsesecurity.com/usage/ Copyright © 2026 Detection Systems & Engineering. All rights reserved.