Knowledge
SPF, DKIM, DMARC, MTA-STS and TLS-RPT in detail – with RFC references and examples.
Why e-mails can be forgedSMTP does not authenticate senders. Envelope From, header From and display name in detail – and where SPF, DKIM and DMARC come in.SPF – Sender Policy FrameworkSPF according to RFC 7208 – syntax, evaluation, lookup limits, qualifiers, alignment with DMARC and typical errors in include chains.DKIM – DomainKeys Identified MailDKIM according to RFC 6376 – signature header, selectors, canonicalisation, keys, algorithms, alignment with DMARC and typical errors.DMARC – policy, alignment and reportsDMARC according to RFC 9989/9990 (previously RFC 7489) – tags, alignment, organisational domain, policies, pct and t, aggregate reports and external report destinations.The interplay of SPF, DKIM and DMARCOrder of checks at the recipient, DMARC decision logic, Authentication-Results and four worked cases with header fields and report rows.Transport encryption – MTA-STS, TLS-RPT and DANEMTA-STS according to RFC 8461 and TLS-RPT according to RFC 8460 with DNS records, policy file, modes and pitfalls; distinction from DANE according to RFC 7672.Forwarding, mailing lists, SRS and ARCIndirect mail flows and DMARC – why SPF breaks and DKIM survives, SRS, From rewriting, ARC according to RFC 8617 and how this looks in reports.History of e-mail authenticationFrom RFC 821 via SPF, Sender ID, DomainKeys and IIM to DKIM, DMARC, ARC, MTA-STS and the requirements of Google, Yahoo and Microsoft.Further developments – DMARCbis, BIMI and DKIM2As of October 2026 – RFC 9989/9990/9991 (DMARCbis) with t, np, psd and tree walk; BIMI with VMC and CMC; IETF DKIM2 drafts against replay.igs.ch guide for specialistsVerification, report address, analysis, sender groups, phase logic with periods and criteria, tasks, fallback, MTA-STS hosting and TLS-RPT at igs.ch.Tasks for external parties – process and securityPersonal links, rights of external parties, replies by e-mail, reminders and escalation, and confirmation based on authenticated reports.