{
  "name": "Microsoft Azure tenant restrictions and 5.7.237 bounces across three fleets",
  "page": "https://warminboxes.com/research/microsoft-azure-tenant-crackdown",
  "fieldwork": "20 October to 8 November 2026",
  "license": "https://creativecommons.org/licenses/by/4.0/",
  "attribution": "WarmInboxes.com",
  "generated": "2026-11-11",
  "id": "WI-RESEARCH-2026-004",
  "bounce_code": "550 5.7.237",
  "block_code": {
    "code": "550 5.7.708",
    "text": "Service unavailable. Access denied, traffic not accepted from this IP",
    "seen_on": "the worst-affected customer accounts: the tenant's outbound refused outright"
  },
  "first_reported": "2026-10-29",
  "diagnosis": {
    "tenant_age_days": "10 to 14",
    "statement": "Microsoft appears to be restricting cold outbound on tenants younger than about 10 to 14 days; domains on older tenants performed normally on the same sequencer IPs.",
    "basis": "Diagnosis from the affected accounts, not a counted split by tenant age."
  },
  "notes": [
    "Microsoft has published no documentation for 5.7.237 that we could find as of 6 November 2026; this records what the fleets did, not what the code means.",
    "Three segments. segment_1 is read from the tenants; its fleet_totals are calculated from the tenant count and averages (formula given), with sends as a ceiling. segment_2 is read from Microsoft Exchange records for the 142 tenants that were hitting 5.7.708 when the October data was pulled: Microsoft records of failed sends (no send counts), two windows with full send counts, hourly checks of Microsoft bounce notices and a licence check; the sources overlap in time and are never added together. segment_3 (our agency fleet) is read from the sequencer."
  ],
  "segment_3_agency_fleet": {
    "label": "Segment 3: our own agency fleet (two workspaces)",
    "window": "26 October to 5 November 2026",
    "inboxes": 12103,
    "total": {
      "sent": 19876,
      "bounced": 188,
      "bounce_rate_pct": 0.9459
    },
    "before_oct26_30": {
      "sent": 6562,
      "bounced": 41,
      "bounce_rate_pct": 0.6248
    },
    "after_nov2_5": {
      "sent": 13201,
      "bounced": 144,
      "bounce_rate_pct": 1.0908
    },
    "days": [
      {
        "date": "2026-10-26",
        "sent": 1587,
        "bounced": 6,
        "bounce_rate_pct": 0.3781
      },
      {
        "date": "2026-10-27",
        "sent": 496,
        "bounced": 4,
        "bounce_rate_pct": 0.8065
      },
      {
        "date": "2026-10-28",
        "sent": 2711,
        "bounced": 21,
        "bounce_rate_pct": 0.7746
      },
      {
        "date": "2026-10-29",
        "sent": 1369,
        "bounced": 8,
        "bounce_rate_pct": 0.5844
      },
      {
        "date": "2026-10-30",
        "sent": 399,
        "bounced": 2,
        "bounce_rate_pct": 0.5013
      },
      {
        "date": "2026-10-31",
        "sent": 30,
        "bounced": 0,
        "bounce_rate_pct": 0
      },
      {
        "date": "2026-11-01",
        "sent": 83,
        "bounced": 3,
        "bounce_rate_pct": 3.6145
      },
      {
        "date": "2026-11-02",
        "sent": 4976,
        "bounced": 59,
        "bounce_rate_pct": 1.1857
      },
      {
        "date": "2026-11-03",
        "sent": 3338,
        "bounced": 36,
        "bounce_rate_pct": 1.0785
      },
      {
        "date": "2026-11-04",
        "sent": 2491,
        "bounced": 22,
        "bounce_rate_pct": 0.8832
      },
      {
        "date": "2026-11-05",
        "sent": 2396,
        "bounced": 27,
        "bounce_rate_pct": 1.1269
      }
    ],
    "workspaces": [
      {
        "workspace": "Workspace A",
        "sent": 12240,
        "bounced": 133,
        "bounce_rate_pct": 1.0866,
        "share_of_bounces_pct": 70.7447
      },
      {
        "workspace": "Workspace B",
        "sent": 7636,
        "bounced": 55,
        "bounce_rate_pct": 0.7203,
        "share_of_bounces_pct": 29.2553
      }
    ],
    "configurations": [
      {
        "inboxes_per_domain": "100",
        "sent": 14120,
        "bounced": 152,
        "bounce_rate_pct": 1.0765,
        "share_of_bounces_pct": 80.8511
      },
      {
        "inboxes_per_domain": "50",
        "sent": 4197,
        "bounced": 23,
        "bounce_rate_pct": 0.548,
        "share_of_bounces_pct": 12.234
      },
      {
        "inboxes_per_domain": "25",
        "sent": 1548,
        "bounced": 13,
        "bounce_rate_pct": 0.8398,
        "share_of_bounces_pct": 6.9149
      },
      {
        "inboxes_per_domain": "1-3",
        "sent": 11,
        "bounced": 0,
        "bounce_rate_pct": 0,
        "share_of_bounces_pct": 0
      }
    ]
  },
  "segment_1": {
    "label": "Segment 1: customer tenants at 25 users per tenant and domain",
    "counted": {
      "tenants_at_least": 1500,
      "observed_days": 21,
      "avg_sends_per_tenant_active_day": 76,
      "peak_tenant_day": 162,
      "bounce_rate_pct_range": [
        1.4,
        2.1
      ],
      "tenant_blocks": 0,
      "licence_wipes": 0
    },
    "fleet_totals": {
      "window": "26 October to 6 November 2026",
      "formula": "1,500 tenants × 76 sends × 12 days",
      "sends_ceiling": 1368000,
      "bounces_range": [
        19152,
        28728
      ],
      "basis": "Every tenant at its active-day average on every day of the window, so the sends are a ceiling and the tenant count a floor."
    }
  },
  "segment_2": {
    "label": "Segment 2: customer tenants at 50 or 100 users per tenant and domain",
    "window": "20 October to 8 November 2026",
    "tenants": 142,
    "tenants_by_users": {
      "50": 73,
      "100": 69
    },
    "cohort": "The tenants that were hitting 5.7.708 when the October data was pulled, fixed there; it shows how hard and for how long, not how many dense tenants were hit.",
    "earliest_evidence": "20 October 2026",
    "observed": "Microsoft refused their outbound with 5.7.708 from at least 20 October; in the worst window half of everything they sent bounced, and by 1 November they were back under 1%.",
    "archive_days": [
      {
        "date": "2026-10-20",
        "failed_recipients": 13790,
        "code_5_7_708": 13751
      },
      {
        "date": "2026-10-21",
        "failed_recipients": 9514,
        "code_5_7_708": 9432
      },
      {
        "date": "2026-10-22",
        "failed_recipients": 10828,
        "code_5_7_708": 10710
      },
      {
        "date": "2026-10-23",
        "failed_recipients": 17249,
        "code_5_7_708": 17095
      },
      {
        "date": "2026-10-24",
        "failed_recipients": 11590,
        "code_5_7_708": 11438
      },
      {
        "date": "2026-10-25",
        "failed_recipients": 14407,
        "code_5_7_708": 14229
      },
      {
        "date": "2026-10-26",
        "failed_recipients": 9946,
        "code_5_7_708": 9682
      },
      {
        "date": "2026-10-27",
        "failed_recipients": 4786,
        "code_5_7_708": 4126
      },
      {
        "date": "2026-10-28",
        "failed_recipients": 10761,
        "code_5_7_708": 9167
      },
      {
        "date": "2026-10-29",
        "failed_recipients": 14288,
        "code_5_7_708": 13170
      },
      {
        "date": "2026-10-30",
        "failed_recipients": 446,
        "code_5_7_708": 444
      }
    ],
    "traces": [
      {
        "window": "Oct 27–30",
        "from": "2026-10-27",
        "to": "2026-10-30",
        "tenants": 59,
        "sent": 55191,
        "delivered": 28096,
        "bounced": 27067,
        "bounce_rate_pct": 49.0424,
        "code_5_7_708": 26750,
        "median_tenant_bounce_pct": 52,
        "tenants_over_40_pct": 42,
        "tenants_under_2_pct": 0,
        "median_sends_per_tenant_day": 220
      },
      {
        "window": "Nov 1–2",
        "from": "2026-11-01",
        "to": "2026-11-02",
        "tenants": 135,
        "sent": 170290,
        "delivered": 167672,
        "bounced": 1595,
        "bounce_rate_pct": 0.9366,
        "code_5_7_708": 966,
        "median_tenant_bounce_pct": 0.3,
        "tenants_over_40_pct": 1,
        "tenants_under_2_pct": 132,
        "median_sends_per_tenant_day": 600
      }
    ],
    "same_tenants_in_both_traces": {
      "tenants": 52,
      "before": {
        "sent": 49954,
        "bounced": 24225,
        "bounce_rate_pct": 48.4946
      },
      "after": {
        "sent": 70446,
        "bounced": 1214,
        "bounce_rate_pct": 1.7233
      }
    },
    "by_size_oct27_30": [
      {
        "users_per_tenant": 50,
        "tenants": 31,
        "sent": 41057,
        "bounced": 20488,
        "bounce_rate_pct": 49.9014,
        "median_sends_per_tenant_day": 465
      },
      {
        "users_per_tenant": 100,
        "tenants": 28,
        "sent": 14134,
        "bounced": 6579,
        "bounce_rate_pct": 46.5473,
        "median_sends_per_tenant_day": 144
      }
    ],
    "watch": [
      {
        "date": "2026-10-31",
        "tenants_with_5_7_708": 24,
        "tenants_read": 126
      },
      {
        "date": "2026-11-01",
        "tenants_with_5_7_708": 3,
        "tenants_read": 125
      },
      {
        "date": "2026-11-02",
        "tenants_with_5_7_708": 1,
        "tenants_read": 125
      },
      {
        "date": "2026-11-03",
        "tenants_with_5_7_708": 0,
        "tenants_read": 125
      },
      {
        "date": "2026-11-04",
        "tenants_with_5_7_708": 0,
        "tenants_read": 125
      },
      {
        "date": "2026-11-05",
        "tenants_with_5_7_708": 0,
        "tenants_read": 125
      },
      {
        "date": "2026-11-06",
        "tenants_with_5_7_708": 0,
        "tenants_read": 125
      },
      {
        "date": "2026-11-07",
        "tenants_with_5_7_708": 0,
        "tenants_read": 125
      },
      {
        "date": "2026-11-08",
        "tenants_with_5_7_708": 0,
        "tenants_read": 125
      }
    ],
    "licences": {
      "read_on": "3 November 2026",
      "enabled": 135,
      "suspended": 0,
      "not_verified": 7
    },
    "dates": "As the Exchange traces recorded them, India Standard Time."
  }
}