Deliverability briefing, Tuesday, 1 September 2026
Microsoft 365 outage causes auth failures for hours
Microsoft 365, the email service millions of companies use, broke for hours yesterday. BleepingComputer and TechCrunch both reported sign-in failures and delayed or failed email, and Microsoft said it was testing a fix, per TechCrunch. If your prospects use Microsoft 365, expect some replies from yesterday to have landed late.
Inbox Rules Index
499 of 499 companies checked, Tuesday, 1 September 2026
Every morning we look up the published email settings of the same 499 real companies, the kind you send cold email to. This is what they have set up, not a score on your own sending.
Today's check of 499 business companies found 88.4% block mail that fakes their own name, unchanged from yesterday and up 0.6 percentage points since 10 August. That number is about how these companies protect themselves, not about how your cold email gets treated. What actually reads your message is the gateway sitting in front of them: Proofpoint in front of 33.9% of the panel, Microsoft 365 in front of 26.1%, Google Workspace in front of 18.8%.
What this means for your sending
Proofpoint screens more of these companies than anything else, at 33.9%, so it is the filter most of your cold email actually meets. 6.2% ask senders for an encrypted connection, so an expired or mismatched certificate on your sending server can stop mail reaching them at all. 2.4% cannot receive email at all, which is dead weight on any list that includes them. The rest is about how these companies stop others forging their address. It is a good sign of how seriously they run email security, but it is not what decides where your mail lands: that is judged against your own domain's records.
Whose spam filter your email meets
| Proofpoint | 33.9% | |
| Microsoft 365 | 26.1% | |
| Google Workspace | 18.8% | |
| Their own servers, or unknown | 9.6% | |
| Mimecast | 4% | |
| Cisco Secure Email | 3.8% |
Proofpoint screens about one in every 3 of these companies, more than any other filter. This is the software that reads your email before a person does, and it is the part of this briefing that most directly decides whether you land.
Which industries guard their name hardest (companies checked)
| Software (126) | 97.6% | |
| Finance (54) | 94.4% | |
| Services (28) | 92.9% | |
| Healthcare (47) | 89.4% | |
| Logistics (17) | 88.2% | |
| Retail (50) | 88% | |
| Travel (25) | 88% | |
| Energy (24) | 87.5% | |
| Media (26) | 84.6% | |
| Telecoms (30) | 80% | |
| Industrial (44) | 79.5% | |
| Schools and universities (28) | 57.1% |
Software guards its name hardest: 97.6% block mail faking their address. Schools and universities least, at 57.1%, a gap of 40.5 points. A high number means that industry runs email security tightly, so expect your own setup to be looked at more closely there.
All 499 of the 499 companies we check answered today. The same real companies every morning, looked up in public DNS. This is what the people you email have set up, not a score on your own sending.
What happened
Massive Microsoft 365 outage causes auth issues, service failures
BleepingComputer reported Microsoft was investigating a widespread issue causing sign-in failures, email delays and other problems for Exchange Online customers. TechCrunch said Microsoft was testing a fix for the hours-long Outlook trouble. If your prospects run Microsoft 365, some of the mail you sent or replies you were expecting may have been delayed or dropped during the outage. Check any campaign that ran through that window before you conclude a message went to spam: it may simply not have arrived yet.
3 outlets: BleepingComputerTechCrunchiTWire
What these numbers mean
Did the Microsoft 365 outage affect my cold email?
It could have, if your prospects use Microsoft 365. BleepingComputer and TechCrunch reported sign-in failures and delayed or failed email during the outage, so replies or opens from that window may show up late rather than never.
What does today's 88.4% enforcement number actually tell me?
It tells you how many of the 499 companies checked today block mail that fakes their own name, not how your cold email gets treated when it lands in their inbox. That number moved up 0.6 percentage points since 10 August and is unchanged from yesterday.
Which gateway is most likely to be reading my cold email?
Proofpoint is the most common gateway, sitting in front of 33.9% of the 499 companies checked. Microsoft 365 is next at 26.1%, and Google Workspace follows at 18.8%.
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