Microsoft does not publish an Outlook user count, so anyone asking how many people use Outlook has to work from license data. The closest figures are 450 million-plus paid Microsoft 365 commercial seats and nearly 95 million Microsoft 365 consumer subscribers. This guide separates those business and personal numbers, then covers seat growth through September 2026, email-open share, Copilot adoption, security fixes, outages, and the new Outlook timeline.
How Many People Use Outlook
How Many Outlook Users Are Business vs Personal?
Microsoft reports paid licenses, not Outlook users. Outlook ships in Microsoft 365 commercial plans and in Microsoft 365 Personal and Family, which makes those two counts the closest public proxies.
The two figures measure different things and should not be added together. Free Outlook.com accounts appear in neither.
Business Accounts: 450 Million-Plus Paid Seats
Paid Microsoft 365 commercial seats passed 450 million in the quarter ended December 31, 2025, up 6% year over year, Microsoft said on its January 28, 2026 earnings call. No newer absolute count has been given.
A seat is a paid user license. It does not confirm the holder opens Outlook. For revenue and segment data beyond email, see these Microsoft company-wide figures.
Source: Microsoft FY26 Q2 earnings call, quarter ended December 31, 2025
Personal Accounts: Nearly 95 Million Subscribers
Satya Nadella put Microsoft 365 consumer subscribers at nearly 95 million on the April 29, 2026 call. Subscriber growth held at 7% in the March, June and September 2026 quarters.
Revenue has grown faster than subscriptions. Microsoft credits higher revenue per user, and says growth is slowing as last year’s price increase leaves the comparison.
| Quarter | Microsoft 365 consumer cloud revenue growth (YoY) |
|---|---|
| Q3 FY26 (ended Mar 2026) | 33% |
| Q4 FY26 (ended Jun 2026) | 24% |
| Q1 FY27 (ended Sep 2026) | 17% |
| Q2 FY27 (ending Dec 2026), Microsoft guidance | Low teens |
Source: Microsoft earnings calls and FY27 Q1 press release, quarters ended March 2026 to September 2026
5% Seat Growth Marks a Slowdown in Outlook’s Business Base
Microsoft 365 commercial seats grew 5% in the quarter ended September 30, 2026. On the same restated basis, growth ran between 6% and 7% through fiscal 2026.
That restated basis is new. From fiscal 2027, the metric also counts paid seats from GitHub’s developer platform, so it no longer tracks Office and Outlook licenses alone.
CFO Amy Hood linked the 5% reading partly to weaker sales execution in Microsoft 365 E3 and standalone SKUs. Small business and frontline worker plans drove most of the growth.
Under the old definition, seat growth printed 6% in every fiscal 2026 quarter. Revenue per seat is rising faster than seat counts.
| Quarter | Microsoft 365 commercial cloud revenue growth (YoY, restated) |
|---|---|
| Q1 FY26 (ended Sep 2025) | 18% |
| Q2 FY26 (ended Dec 2025) | 17% |
| Q3 FY26 (ended Mar 2026) | 20% |
| Q4 FY26 (ended Jun 2026) | 16% |
| Q1 FY27 (ended Sep 2026) | 17% |
Source: Microsoft Form 8-K FY27 investor metrics and FY27 Q1 earnings release, quarters ended September 2025 to September 2026
Outlook Email Client Market Share by Opens
Litmus counted over 1.5 billion tracked email opens in September 2026. Outlook desktop ranked third at 3.48%, and Outlook.com ranked sixth at 0.29%.
Litmus reports the two Outlook lines separately. Desktop covers Outlook for Windows from the 2000-2003 versions onward plus Outlook for macOS; Outlook.com covers webmail opened in any browser.
These shares show where tracked emails were opened, not who owns an account. The sample comes from Litmus customers’ own sends, which skews it toward brand marketing messages rather than workplace mail.
Apple’s 76.56% includes Mail Privacy Protection opens, which Litmus does not treat as reliable. Litmus also says image blocking can over- or under-represent some clients.
Source: Litmus Email Client Market Share, September 2026
Is Copilot Now Used as Often as Outlook?
Nadella said in April 2026 that Microsoft 365 Copilot’s weekly engagement had reached Outlook’s level. By July 2026, he put average weekly engagement on par with Outlook and Teams.
Paid Copilot seats passed 30 million by the July 29, 2026 call, double the 15 million reported in January. Microsoft gave no updated count in October 2026.
For the September 2026 quarter, Microsoft instead reported Copilot daily users up nearly 50% quarter over quarter and over 5x year over year. Customers with more than 50,000 Copilot seats rose over 8x.
Consumer assistants are measured differently; Gemini’s adoption data covers the main Google rival.
Source: Microsoft earnings calls, January 28, April 29, July 29 and October 28, 2026
Security Fixes and Exchange Outages Hitting Outlook in 2026
| CVE | Severity | CVSS | Microsoft exploitation assessment |
|---|---|---|---|
| CVE-2026-70242 | Critical | 9.8 | Exploitation Less Likely |
| CVE-2026-70291 | Critical | 9.8 | Exploitation Less Likely |
| CVE-2026-88156 | Critical | 9.8 | Exploitation Less Likely |
| CVE-2026-97016 | Critical | 9.8 | Exploitation Less Likely |
| CVE-2026-97749 | Critical | 9.8 | Exploitation Less Likely |
Source: Rapid7 Patch Tuesday analysis of Microsoft data, October 2026
Microsoft’s October 13, 2026 Patch Tuesday fixed all five Outlook remote code execution flaws above. None was publicly disclosed before release.
For CVE-2026-70291 and CVE-2026-88156, Microsoft lists the Preview Pane as an attack vector, according to CrowdStrike. Viewing a crafted message could be enough.
Source: CrowdStrike Patch Tuesday analysis, October 2026
Exchange Online Incident EX1464935
The incident began at 10:08 AM CDT on August 31, 2026. Microsoft listed authentication errors, failed or incomplete mailbox searches, and problems in Exchange admin tools.
Microsoft later confirmed the faulty authentication component affected services beyond Exchange Online, tracked as MO1465074. At 7:01 PM CDT the same day, engineers were still restarting affected infrastructure.
Source: Microsoft service health notice posted on Microsoft Q&A, August 31, 2026
When Does New Outlook Become the Default?
| Stage | Timing | What changes |
|---|---|---|
| Opt-in | Current stage | Users choose whether to try new Outlook |
| Enterprise opt-out | March 2027 (was April 2026) | New Outlook becomes the default; users and admins can switch back |
| Cutover | No earlier than March 2028 | Follows at least 12 months’ notice after opt-out |
| Classic Outlook support | At least 2029 | Existing perpetual and subscription installs stay supported |
Source: Microsoft 365 message center notice MC949965, via Directions on Microsoft, 2026
The March 2028 floor is Directions on Microsoft’s reading of the 12-month notice rule, not a date Microsoft announced. Timelines for GCC High and DoD tenants will come later, Microsoft said.
FAQs
How many people use Outlook in 2026?
Microsoft does not publish one. Its nearest figures are over 450 million paid Microsoft 365 commercial seats (December 2025 quarter) and nearly 95 million Microsoft 365 consumer subscribers (April 2026). Free Outlook.com accounts are not counted.
Is Outlook more popular than Gmail?
By tracked opens, no. Litmus recorded Gmail at 16.10% and Outlook desktop at 3.48% of email opens in September 2026. Those shares show where emails were opened, not account ownership.
Does new Outlook become mandatory in 2027, as Reddit users often ask?
No. March 2027 starts the enterprise opt-out stage, moved from April 2026 under notice MC949965. New Outlook becomes the default, but users can switch back. Classic Outlook stays supported until at least 2029.
Was Outlook down in 2026?
Yes. Exchange Online incident EX1464935 began August 31, 2026, causing authentication errors and mailbox search failures. Microsoft confirmed the faulty authentication component also hit other services, tracked as MO1465074.
Is Outlook’s business user base still growing?
Slowly. Microsoft 365 commercial seats grew 5% in the quarter ended September 30, 2026, down from 7% in the June 2026 quarter on the same restated basis, which now includes GitHub seats.
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