{
 "metric": "mx-tls-cert",
 "segment": "gb-small",
 "anchor": "company",
 "label": "UK small companies",
 "population": "UK small companies",
 "states": [
  "valid",
  "hostname_mismatch",
  "self_signed",
  "expired"
 ],
 "quiet_failure_states": [
  "self_signed",
  "expired"
 ],
 "measurement": "Complete STARTTLS, inspect the leaf certificate. Denominator: MXs offering STARTTLS.",
 "why_it_matters": "SMTP TLS is *opportunistic* (RFC 7435) — senders accept any certificate — so an invalid certificate still encrypts but authenticates nothing, leaving the connection open to interception. It only becomes a hard failure under DANE or MTA-STS `enforce`.",
 "limits": "Honesty demands the split. Because opportunistic TLS tolerates mismatches, only `self_signed` and `expired` are counted as the quiet failure; `hostname_mismatch` is reported but **not** counted.",
 "data_tier": "smtp",
 "population_predicate": "has_mx",
 "entity_type": "domain",
 "kind": "failure",
 "latest": {
  "day": "2026-08-14",
  "n": 394,
  "qf_pct": 1.52,
  "ci": [
   0.7,
   3.28
  ],
  "dist": {
   "valid": 91.88,
   "hostname_mismatch": 6.6,
   "self_signed": 0.76,
   "expired": 0.76
  },
  "snapshot": "uk-companies-house-per600-seed20260728"
 },
 "series": [
  {
   "day": "2026-08-02",
   "n": 346,
   "qf_pct": 2.31,
   "ci": [
    1.18,
    4.5
   ],
   "dist": {
    "valid": 92.77,
    "hostname_mismatch": 4.91,
    "self_signed": 1.45,
    "expired": 0.87
   },
   "snapshot": "uk-companies-house-per300-seed20260728"
  },
  {
   "day": "2026-08-04",
   "n": 396,
   "qf_pct": 1.52,
   "ci": [
    0.7,
    3.27
   ],
   "dist": {
    "valid": 91.92,
    "hostname_mismatch": 6.57,
    "self_signed": 0.76,
    "expired": 0.76
   },
   "snapshot": "uk-companies-house-per600-seed20260728"
  },
  {
   "day": "2026-08-05",
   "n": 397,
   "qf_pct": 1.26,
   "ci": [
    0.54,
    2.91
   ],
   "dist": {
    "valid": 91.94,
    "hostname_mismatch": 6.8,
    "self_signed": 0.5,
    "expired": 0.76
   },
   "snapshot": "uk-companies-house-per600-seed20260728"
  },
  {
   "day": "2026-08-07",
   "n": 391,
   "qf_pct": 1.02,
   "ci": [
    0.4,
    2.6
   ],
   "dist": {
    "valid": 92.07,
    "hostname_mismatch": 6.91,
    "self_signed": 0.51,
    "expired": 0.51
   },
   "snapshot": "uk-companies-house-per600-seed20260728"
  },
  {
   "day": "2026-08-14",
   "n": 394,
   "qf_pct": 1.52,
   "ci": [
    0.7,
    3.28
   ],
   "dist": {
    "valid": 91.88,
    "hostname_mismatch": 6.6,
    "self_signed": 0.76,
    "expired": 0.76
   },
   "snapshot": "uk-companies-house-per600-seed20260728"
  }
 ],
 "license": "CC BY 4.0",
 "source": "https://quietfailures.com/datasets/mx-tls-cert/gb-small"
}