herder-institut.de

SOA · negative caching TTL (minimum) 1m is outside 5m–1d (RFC 2308 recommends 1–3 hours). Current values: refresh 1d, retry 1h, expire 1000h, negative TTL 1m.

DNSSEC · The zone is not signed with DNSSEC, so answers can be spoofed. Enable DNSSEC at your DNS provider and publish the DS record at your registrar.

DMARC · DMARC policy is set to 'quarantine'. Consider upgrading to 'reject' for stronger protection once you've verified legitimate emails are passing authentication.

DKIM · The _domainkey name exists but no DKIM key was found under the common selectors. Selectors are provider-specific; check yours with -selector.

DNSSEC · DNSSEC is not enabled for this domain. Consider enabling DNSSEC to protect against DNS spoofing attacks.

MX · The following MX hosts could not be resolved to IPv6 addresses: a2111.mx.srv.dfn.de, b2111.mx.srv.dfn.de, c2111.mx.srv.dfn.de

TLS · MTA-STS is not configured, so other mail servers fall back to unencrypted delivery when TLS fails or is stripped by an attacker. Publish a _mta-sts TXT record and a policy at https://mta-sts.<domain>/.well-known/mta-sts.txt.

TLS · MTA-STS or DANE is used without TLS-RPT, so you get no reports when senders fail to deliver because of TLS problems. Publish _smtp._tls TXT "v=TLSRPTv1; rua=mailto:...".