Deliverability briefing, Thursday, 3 September 2026
Microsoft update breaks Outlook and Teams on Arm PCs
Microsoft's latest update is stopping Outlook and Teams from opening on Arm-based Windows PCs. The Register and BleepingComputer both reported the failures, which follow updates released after August's Patch Tuesday. If a contact reaches for Outlook today and nothing happens, that's likely why, not your email.
Inbox Rules Index
499 of 499 companies checked, Thursday, 3 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 companies found 88.4% now block mail that forges their own address, unchanged from yesterday and up 0.6 percentage points from the 10 August baseline. That's a measure of how tightly these companies guard their own name, not a signal about how they'll treat your cold email into their inbox.
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.
Who changed their setup
| zoho.com | Sender list: locked list → nothing published | looser |
1 of these companies changed their email setup since Wednesday, 2 September 2026: 1 got looser. If any are on your list, the stricter ones are running their email security actively.
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
Microsoft update disarms Outlook and Teams on Arm PCs
The Register and BleepingComputer reported that a Microsoft update is causing Teams and the new Outlook to crash or fail to launch on Arm-based Windows PCs. BleepingComputer says the trouble started with updates released since August's Patch Tuesday, and Microsoft is working on a fix. If a prospect on one of these machines misses your email or a meeting invite, it's probably this, not your sending setup. Wait a day or two before assuming they ignored you.
2 outlets: The RegisterBleepingComputer
Microsoft prepares final phase of Exchange Web Services retirementAnnounced by the provider
Microsoft says Exchange Web Services, an older way outside apps connect to Outlook and Exchange inboxes, is entering the final phase of its retirement. The company has spent years pushing tools over to Microsoft Graph and other newer connections instead, according to its Exchange Team blog. If you rely on a sending, warmup, or inbox-checking tool that still talks to Outlook over Exchange Web Services, ask your vendor whether they have already moved to the newer connection, because Microsoft's retirement clock is now in its last stage.
Source: Microsoft Exchange Team Blog
What these numbers mean
Why did Outlook or Teams stop opening for some contacts today?
Microsoft pushed an update that crashes or blocks Teams and the new Outlook from launching on Arm-based Windows PCs, according to The Register and BleepingComputer. BleepingComputer reports the issue follows updates released since August's Patch Tuesday and says Microsoft is working on a fix.
What does 88.4% DMARC enforcement mean for my cold email?
Today's panel found 88.4% of 499 companies enforce settings that block mail forging their own name, unchanged from yesterday and up 0.6 percentage points from the 10 August baseline. That number reflects how tightly a company guards its own domain, it says nothing about whether your unauthenticated mail into their inbox will be blocked.
Which company checks my cold email before a person sees it?
Most likely Proofpoint, the gateway in front of 33.9% of the 499 companies measured today, ahead of Microsoft 365 at 26.1% and Google Workspace at 18.8%. A domain behind Proofpoint or Mimecast usually still runs on Microsoft or Google behind that, but the panel only sees the gateway.
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