If you are comparing ProtonMail vs Outlook for privacy, start with who you want to keep out of your messages. Proton (it now writes the name as Proton Mail) builds the service so that even Proton cannot read your stored mail. Outlook sits inside Microsoft 365, where admin control and integration matter more. I work with Outlook and Exchange Online at work, but I have not run a Proton Mail account myself. So this comes from Proton’s and Microsoft’s own documentation, checked in October 2026.
Quick Answer: Proton Mail is better if you want only you and the recipient to read a message, and you can live with fewer features. Outlook is better if you work in Microsoft 365 and need admin controls, Office integration and a large mailbox. If you want both, Proton’s Bridge only works with classic Outlook, not new Outlook for Windows.
Proton Mail vs Outlook at a Glance
The table keeps only the points that change the decision. The sections after it explain each one.
| Proton Mail | Outlook | |
|---|---|---|
| Company | Proton AG, Switzerland | Microsoft |
| Stored mail | Zero-access encryption, Proton says it cannot read it | Not zero-access. Encrypt a message yourself with Purview Message Encryption or S/MIME |
| Free mailbox | 1 GB, 150 messages a day | 15 GB (Outlook.com), with ads |
| Paid mailbox | Mail Plus 15 GB, Proton Unlimited 500 GB | 100 GB with a Microsoft 365 subscription |
| In Outlook desktop | Through Bridge, paid plan only, classic Outlook only | Native |
| Inbox sorting | Categories (Primary, Social, Promotions, Newsletters) | Focused Inbox (Focused and Other) |
ProtonMail vs Outlook Security: What Proton Mail Actually Encrypts
Proton Mail started in 2014, founded by scientists who met at CERN, and the company is based in Switzerland. The apps are open source and Proton publishes independent audit reports. The latest one I found covers the new Proton Mail and Proton Calendar, done by Securitum, with no major issues found. That is Proton’s own claim, see their security audit page.
Whether a message is end-to-end encrypted depends on who you write to. Proton explains it this way:
- Mail between two Proton addresses is end-to-end encrypted.
- Mail to another provider (Gmail, Outlook.com, a company domain) travels with TLS, the normal transport encryption most providers support. After delivery it is not end-to-end encrypted, so the recipient’s provider may be able to read it.
- Mail to another provider can still be end-to-end encrypted if you send a password-protected message, or if the other side uses PGP.
- Everything in your own Proton inbox has zero-access encryption. In Proton’s words, nobody else can access it, not even Proton.
Two limits are easy to miss. Subject lines are not end-to-end encrypted. OpenPGP keeps the subject in the header, and Proton suggests generic subject lines for sensitive mail.
The second is the “no IP logs” line you see in many reviews. In September 2021 a Swiss order, passed on from French police through Europol, forced Proton to log the IP address of one French activist’s account. Proton said it had no legal way to refuse. A gag order also stopped it telling the user at the time (The Record has the details).
Switzerland is also working on a surveillance ordinance (the VÜPF revision). Reports say it would reach smaller services, with identity checks and metadata retention. Proton has started moving some infrastructure out of the country, Lumo first, and says it is not leaving Switzerland (heise report). The proposal is under review. Check where it stands before you pick Proton for Swiss law alone.
One correction to older posts, including the first version of this one. Secure Core (the multi-server routing) belongs to Proton VPN, not Proton Mail. Proton VPN is a separate product (Proton Unlimited bundles it), and Secure Core does nothing for your email.
What Outlook Gives You Instead
Outlook is the client and Microsoft runs the mailbox behind it. You get security controls and admin tooling, and you choose which messages to encrypt instead of having every stored message locked away from the provider.
The steps to encrypt a message depend on the client (Microsoft’s S/MIME and Purview page lists all of them):
- New Outlook: in the message, select Options > Encrypt for Purview Message Encryption. For S/MIME, select Options > More Options and check Encrypt this message (S/MIME).
- Classic Outlook: in the message, select Options > Encrypt.
- Outlook on the web: select More options > Message options and check Encrypt this message (S/MIME).
You need a qualifying Microsoft 365 subscription. New Outlook supports Purview Message Encryption only when your email server has an Office 365 Enterprise E3 licence. Otherwise use S/MIME, which needs a certificate set up on the computer. A recipient on another mail service gets a message with instructions on how to open the encrypted one.
Every cloud mailbox in Exchange Online has built-in spam, phishing and malware filtering. Microsoft Defender for Office 365 Plan 1 (Safe Links, Safe Attachments, impersonation protection) comes with subscriptions like Microsoft 365 Business Premium and E3/G3. Plan 2 (Threat Explorer, automated investigation) comes with E5. Microsoft sends Outlook.com users with a Microsoft 365 subscription to a separate page for Safe Links and advanced attachment scanning, and the plan ladder is in its Defender for Office 365 overview.
Free Outlook.com gives 15 GB and shows ads, and Microsoft says it does not read your email contents to pick them. A Microsoft 365 subscription raises the mailbox to 100 GB (Outlook.com storage limits).
For work, Microsoft 365 Business Basic, Standard and Premium moved from a 50 GB to a 100 GB primary mailbox, rolling out in 2026. Standalone Exchange Online Plan 1 stays at 50 GB (Exchange team blog). To check your own, see how to see your Outlook mailbox size.
Does Proton Mail Work with Outlook?
Yes, on Windows and Mac, but only through Proton Mail Bridge, and on Windows only with classic Outlook. Bridge runs on your computer as a local IMAP and SMTP server (the protocols Outlook uses now include both), so desktop clients like Outlook, Thunderbird and Apple Mail can read your encrypted mail. It needs a paid Proton plan. It runs on Windows, macOS and Linux, and there is no version for phones (Proton’s Bridge page).
New Outlook for Windows cannot use it. New Outlook syncs your mail through Microsoft’s cloud, Bridge needs a direct connection from the same computer, and the sign-in fails with an error. Proton’s own Bridge and new Outlook guide says to switch back to classic Outlook with the New Outlook toggle. Proton also says it has no current plans to break Outlook for Mac the same way.
This matters because Microsoft is moving people to new Outlook. Classic Outlook is supported until at least 2029. For Microsoft 365 enterprise users the automatic move (the opt-out phase) was pushed to March 2027. There is no cutover date yet, and Microsoft promises at least 12 months notice. Home users who only have personal accounts and a Microsoft 365 Personal or Family subscription have been switched automatically since October 2024.
If Outlook flips you to new Outlook, Bridge stops working. To stay on classic, open classic Outlook and go to File > Options > General > New Outlook options, then clear Automatically switch me to new Outlook. Not sure which one you have? Here is how to know if you have new Outlook or classic Outlook, and how to switch back to classic Outlook if you already moved.
Inbox and Apps: Focused Inbox vs Proton Categories
Both now sort your inbox for you, in different ways.
What Is Focused vs Other in Outlook?
Focused holds the mail Outlook thinks matters to you, and Other holds the rest. Nothing is deleted, it only sorts. In new Outlook and Outlook on the web you choose Sort messages into Focused and Other, or Don’t sort my messages to turn it off. Right-click a message and select Move, and you can send all future mail from that sender to the tab you want (Microsoft’s Focused Inbox page).
Proton Categories
Proton added Categories in 2026. Mail is sorted into Primary, Social, Promotions and Newsletters, with Transactions and Updates available in settings. Proton says it sorts from metadata without reading the message. Right-click a message and select Move to category… to correct it. To turn it off, open Settings and use Email categories. Primary cannot be turned off (It’s FOSS report).
Proton also lets you use a Gmail address inside Proton Mail. In Settings, open Import via Easy Switch, choose Google and select Connect to Gmail. Mail you send from that address to Proton users is end-to-end encrypted. Mail to anyone else goes through Gmail’s servers without end-to-end encryption, so Google can read it (Proton’s Gmail guide).
On the phone, Outlook for iOS and Android is Microsoft’s app. Old guides still mention Cortana voice commands in it. Microsoft retired Cortana in Outlook mobile in the fall of 2023, and voice search and Play My Emails in June 2024. Proton has its own apps. Bridge is not available on mobile, so the Outlook app is not how you read a Proton inbox.
Pricing and Storage
Prices change and differ by country, so check the official pages before you buy. This is what the US pages showed in October 2026.
- Proton Free: $0, 1 GB, 150 messages a day, 25 MB attachments.
- Mail Plus: $3.99 a month billed yearly ($47.88), 15 GB, 10 addresses, unlimited sending. It is the cheapest plan that includes Bridge.
- Proton Unlimited: $9.99 a month billed yearly ($119.88), 500 GB, with the VPN, Drive and Pass included (Proton pricing).
- Outlook.com free: 15 GB with ads.
- Microsoft 365 Personal: $99.99 a year. Family (up to six people): $129.99 a year.
Microsoft added Copilot to Personal and Family in January 2025 with a price rise. The older no-Copilot “Classic” plans ($69.99 and $99.99) are only offered in some cases (Office Watch’s plan overview). Earlier versions of this post listed euro prices for Proton and a $159.99 standalone Outlook. I could not confirm the standalone price on a Microsoft page, so it is gone.
What Is the Downside of Proton Mail?
You give up size and reach. The free plan is small (1 GB, 150 messages a day). Mail to people outside Proton is not end-to-end encrypted unless you use a password-protected message or PGP, and subject lines never are. Bridge needs a paid plan, works on desktop only, and breaks with new Outlook for Windows.
For a company, the bigger question is control. Before moving a team to any mailbox outside Microsoft 365, I would check retention, eDiscovery, shared mailboxes and mail flow rules first, because those live in Exchange Online.
Is Proton Mail or Outlook More Private?
Proton Mail is more private for the content of your stored mail, because Proton cannot read it and Outlook is not zero-access. Outlook gives you more controls around the mailbox, and you pick which messages to encrypt. So the pick depends on how you work:
- Pick Proton Mail if the content of your personal mail matters most, and the people you write to are on Proton or will open a password-protected message.
- Pick Outlook if you live in Microsoft 365, share calendars and mailboxes at work, and need admin policies. Use Purview Message Encryption or S/MIME for the few messages that are sensitive.
- Use both if you want Proton’s encryption inside Outlook: buy a paid Proton plan, install Bridge, and stay on classic Outlook.
Before you decide, check which Outlook you are running. It decides whether Bridge can work at all.
