{
 "metric": "mx-tls-cert",
 "segment": "gb-companies",
 "anchor": "company",
 "label": "UK companies",
 "population": "UK 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": 1071,
  "qf_pct": 1.59,
  "ci": [
   0.99,
   2.53
  ],
  "dist": {
   "valid": 92.62,
   "hostname_mismatch": 5.79,
   "self_signed": 1.12,
   "expired": 0.47
  },
  "snapshot": "uk-companies-house-per600-seed20260728"
 },
 "series": [
  {
   "day": "2026-08-02",
   "n": 949,
   "qf_pct": 1.69,
   "ci": [
    1.04,
    2.72
   ],
   "dist": {
    "valid": 94.31,
    "hostname_mismatch": 4,
    "self_signed": 0.84,
    "expired": 0.84
   },
   "snapshot": "uk-companies-house-per300-seed20260728"
  },
  {
   "day": "2026-08-04",
   "n": 1074,
   "qf_pct": 1.68,
   "ci": [
    1.06,
    2.63
   ],
   "dist": {
    "valid": 92.83,
    "hostname_mismatch": 5.49,
    "self_signed": 0.93,
    "expired": 0.74
   },
   "snapshot": "uk-companies-house-per600-seed20260728"
  },
  {
   "day": "2026-08-05",
   "n": 1076,
   "qf_pct": 1.67,
   "ci": [
    1.06,
    2.63
   ],
   "dist": {
    "valid": 92.66,
    "hostname_mismatch": 5.67,
    "self_signed": 1.02,
    "expired": 0.65
   },
   "snapshot": "uk-companies-house-per600-seed20260728"
  },
  {
   "day": "2026-08-07",
   "n": 1057,
   "qf_pct": 1.04,
   "ci": [
    0.58,
    1.85
   ],
   "dist": {
    "valid": 93.66,
    "hostname_mismatch": 5.3,
    "self_signed": 0.66,
    "expired": 0.38
   },
   "snapshot": "uk-companies-house-per600-seed20260728"
  },
  {
   "day": "2026-08-14",
   "n": 1071,
   "qf_pct": 1.59,
   "ci": [
    0.99,
    2.53
   ],
   "dist": {
    "valid": 92.62,
    "hostname_mismatch": 5.79,
    "self_signed": 1.12,
    "expired": 0.47
   },
   "snapshot": "uk-companies-house-per600-seed20260728"
  }
 ],
 "license": "CC BY 4.0",
 "source": "https://quietfailures.com/datasets/mx-tls-cert/gb-companies"
}