As of 6 Nov 2026, the panel rates Microsoft 365 Business 3/5 and Proton for Business 3.5/5 in Business Email & Office Suites. Weighted by what each judge cares about, 4 of the 6 judges pick Microsoft 365 Business and 2 pick Proton for Business. Microsoft 365 Business scores higher on 3 of 7 criteria (Calendar, contacts & office apps, Migration, open standards & exit and Mail, domains & deliverability). Proton for Business scores higher on 4 of 7 criteria (European sovereignty, Pricing transparency, Administration, identity & partner management, plus 1 more). Provenance — Microsoft 365 Business: Rest of world; Proton for Business: UK / wider Europe. Ratings are the AI panel’s opinion, formed from public evidence: how scores are made.
Microsoft 365 Business and Proton for Business split this bench. Microsoft 365 Business holds the productivity side: mail and deliverability at 7.0 vs 5.8 and calendar and office at 7.5 vs 6.2, six judges leaning its way on each, plus migration and portability at 7.0 vs 5.7, five judges to one. Proton for Business holds the governance side: security and compliance at 7.3 vs 6.5, where four judges lean Proton and two tie; administration and identity at 7.2 vs 6.3, five lean Proton and one tie; and sovereignty at 6.7 vs 4.5 plus pricing transparency at 7.0 vs 5.8, six judges leaning Proton on each. The weighted totals carry the split through: of five judges with totals shown, the IT administrator, IT service provider and skeptic put Microsoft 365 Business ahead, while the public-sector IT lead and data protection officer put Proton for Business ahead.
Choose Microsoft 365 Business if
You need the office suite itself — documents, spreadsheets and calendars — as the core of the purchase; calendar and office leans Microsoft 365 Business 7.5 to 6.2, six judges to zero.
Your mail operations depend on per-plan limits, quarantine and a hosted Exchange Online setup; mail and deliverability leans Microsoft 365 Business 7.0 to 5.8, six judges to zero.
Your team is moving mail into or out of the platform and wants a documented path both ways; migration and portability leans Microsoft 365 Business 7.0 to 5.7, five judges to one.
You buy the way the IT administrator, the IT service provider or the skeptic does; their weighted totals put Microsoft 365 Business ahead at 6.4 vs 6.3, 6.6 vs 6.4 and 6.5 vs 6.2.
Choose Proton for Business if
You need encryption the provider states it cannot decrypt, backed by ISO 27001 and SOC 2 Type II; security and compliance leans Proton for Business 7.3 to 6.5, four judges lean Proton and two tie.
Your team runs SAML sign-on with Okta or Microsoft Entra ID, three admin roles with a permission matrix, and a SCIM 2.0 API; administration and identity leans Proton for Business 7.2 to 6.3, five judges lean Proton and one tie.
Data sovereignty is your deciding criterion; it leans Proton for Business 6.7 to 4.5, six judges to zero.
You want the steadiest published pricing picture; pricing transparency leans Proton for Business 7.0 to 5.8, six judges to zero.
You buy the way the public-sector IT lead or the data protection officer does; their weighted totals put Proton for Business ahead at 5.9 vs 6.7 and 6.3 vs 7.1.
Read this comparison as one judge. Each weighs the same scores by what they care about.
The Skeptic
Has seen "hosted in Germany" from a provider whose spam filter and support desk sit in the United States, "Exchange-compatible" that meant IMAP with a calendar plug-in, and a first-year price of one euro that became seven. Asks which protocols Outlook really uses, whether the archive would survive a tax audit, what the certification actually covers — and how ten years of mail, calendars and contacts would leave.
Microsoft 365 Business
This judge's pick
Proton for Business
Criterion by criterion
Mail, domains & deliverability
Microsoft 365 Business
A hosted Exchange service with anti-spam and anti-malware across all plans, quarantine an administrator can review, transport and inbox rules, out-of-office replies, distribution groups up to 100,000 members, unlicensed shared and resource mailboxes, and per-plan storage and message limits stated to the megabyte. What I cannot find is the sending side of the story: no custom-domain DNS set-up and no SPF, DKIM, DMARC or MTA-STS documentation on any captured page. The plumbing is documented; the authentication and delivery reputation a sender is judged by is not.
Proton for Business
Custom domains are documented down to the DNS record — an SPF include string, DKIM with a new 2048-bit key every six months, a DMARC TXT — plus catch-all, groups, spam filtering, custom rules and automated replies, with apps on every platform. But Outlook and Thunderbird reach this mail only through the Bridge desktop application speaking IMAP and SMTP; we found no public information on Exchange ActiveSync or native MAPI, on MTA-STS or DANE, on shared mailboxes, or on send and attachment limits, and deliverability is left to the buyer's own Mail Tester run.
Calendar, contacts & office apps
Microsoft 365 Business
Rooms, resource mailboxes, calendar sharing and federated publishing, a global address list with offline address books, and shared mailboxes reachable through the calendar and contacts APIs sit next to Word, Excel, PowerPoint and Outlook for desktop, web and mobile, 1 TB of OneDrive storage, Teams, and ten-plus extra apps in the same plans; add-ins run across Windows, Mac, Android, iOS and the web. We found no public information on browser co-editing, CalDAV or CardDAV, or free/busy lookups across providers — phones here sync through ActiveSync, which is documented.
Proton for Business
The bundle is real: shared calendars with an availability view, appointment scheduling with 25 booking pages, invitations handled from the inbox, external calendar subscriptions, Docs and Sheets co-edited in the browser with collaborators who have no account, Drive storage with password-protected expiring links, and video meetings up to 250 participants with recording. What we found no public information on is CalDAV or CardDAV sync, room and resource booking, delegated calendar access, Outlook calendar and contacts sync, tasks and a company-wide address book — the calendar is documented only inside Proton's own apps.
Security, encryption & compliance archiving
Microsoft 365 Business
The archive would likely survive an audit: auto-expanding archive mailboxes to 1.5 TB, retention labels and policies across Exchange, SharePoint and Teams, legal holds per mailbox, records with proof of disposition for up to seven years, eDiscovery, S/MIME signing and encryption, and deleted-item recovery. But we found no public information on certifications — no ISO 27001, BSI C5 or SOC 2 with scope and auditor — nor on TLS in transit, encryption at rest, enforced two-factor, or a transparency report on authority requests. The compliance tooling is documented; the provider's own audit paper trail is not on these pages.
Proton for Business
End-to-end encryption by default, zero-access storage the provider states it has no means to decrypt, PGP inside Outlook, Apple Mail and Thunderbird, enforced 2FA, open-source apps independently audited, ISO 27001 with a named accreditation body, SOC 2 Type II, and a transparency page stating disclosure only to Swiss authorities. The tax-audit side is thinner: we found no public information on GoBD-compliant archiving, legal hold, eDiscovery, or backup and restore of deleted mail, and the captured pages give different scopes for the ISO 27001 certificate — one says Proton Drive is certified, another says Proton is.
Administration, identity & partner management
Microsoft 365 Business
Administration runs through the Microsoft 365 admin center, the Exchange admin center and remote Windows PowerShell, with full Microsoft Entra ID integration, conditional access and identity protection, Graph REST APIs with SDKs, and PowerShell provisioning of users, groups and teams. Mobile device policies come via ActiveSync, with device and device-deletion limits stated. We found no public information on single sign-on protocols, SCIM provisioning, exportable audit logs, reseller accounts managing several customer organisations, or support response times per plan.
Proton for Business
Three admin roles with a published permission matrix, SAML single sign-on with Okta and Microsoft Entra ID, a documented SCIM 2.0 API covering users and groups down to error codes, security policies including enforced 2FA and Proton Sentinel, an activity monitor admins can export, and an uptime SLA of 99.95% with service credits of 10% and 30%. We found no public information on mobile device policies with remote wipe, reseller or partner accounts managing several customer organisations, or support response times — the SLA covers uptime, and phone support begins at six users.
Migration, open standards & exit
Microsoft 365 Business
Getting in is documented as well as anything I have seen: cutover, staged and hybrid migrations from named Exchange versions, hybrid keeping on-premises and online mailboxes side by side while users move over gradually, IMAP from Gmail and other systems, a PST import service by network upload or drive shipping, Gmail and cross-tenant paths, plus FastTrack and partner help. The way out is one API line on mailbox import and export and the statement that all associated data is deleted when the subscription is cancelled — no data-return period, organisation-wide export format or deletion confirmation documented. And the IMAP route moves mail folders only; contacts and calendar items are left to the user.
Proton for Business
Getting in is Easy Switch over IMAP or a supported provider with guided live support at no extra cost, and mail leaves cleanly: a command-line tool for Windows, macOS and Linux exports everything as EML with JSON metadata, and Bridge pulls the full mailbox to a local client, with deletion of personal data on service cessation stated in the data processing agreement. But the open-source apps come without a self-hosted edition, and we found no public information on export of calendars or contacts in standard formats, on whole-organisation export by an admin, or on CalDAV and CardDAV access; MBOX import needs a detour through Thunderbird local folders and messages invalid per RFC are simply not imported.
European sovereignty
Microsoft 365 Business
The EU Data Boundary is documented with Microsoft datacentres named in fifteen European countries, in scope for tenants that sign up in the EU or EFTA — but the same pages concede that Customer Data, personal data and Professional Services Data will continue to be transferred outside the boundary in limited circumstances, the vendor is a US corporation, and we found no public information on the contracting entity, subprocessors and their locations, a data processing agreement, or security certifications. An on-premises Exchange Server edition is documented too, but that is a separate product, not this cloud suite. European hosting under an American parent with an unnamed chain is part of the chain, not the whole of it.
Proton for Business
Proton AG in Geneva under the non-profit Proton Foundation, data centers exclusively in Europe, a Luxembourg GDPR representative, a published data processing agreement restricting transfers to Switzerland, the EU and adequacy countries, and a subprocessor list with locations — more of the chain is on the table than with most providers. It stops short of the top: the data centres are not named, the contracting entity is Swiss rather than an EU entity, and support and payment run through Zendesk, Atlassian, Stripe, Chargebee and PayPal in the United States and ProtonLabs in Taiwan and North Macedonia, with safeguards stated for some but not all of them.
Pricing transparency
Microsoft 365 Business
Business Basic is published at 6,07 € per user per month with annual billing, Standard and Premium appear only bundled with Copilot at 20,36 € and 27,73 €, all excluding VAT, with a one-month credit-card trial that auto-converts and a 7-day withdrawal right. Mailbox storage per plan, the 50 GB ceiling for unlicensed shared mailboxes, and the fact that rooms and shared mailboxes need no subscription are public, so much of a bill is computable. We found no price for the usage-based advanced AI billing, for extra storage, or for any monthly-payment alternative — the captured pages show annual billing only.
Proton for Business
Both tiers carry public per-user prices with storage — Workspace Standard at €12.99/user per month on yearly billing against €14.99 monthly, Premium at €19.99 against €24.99, "Billed at €155.88 every 12 months. Taxes may apply." — plus monthly, yearly and bi-yearly cycles, VAT treatment including reverse charge for business plans, and a 30-day money-back guarantee with its restrictions spelt out. The soft spot is the extras: we found no public price for the Scribe add-on, extra aliases or extra storage, nonprofit pricing is on request, Enterprise is "Let's talk", and we found no public information on minimum users or contract term.
Sovereignty, side by side
Dimension
Microsoft 365 Business
Proton for Business
Legal entity
Not determined
Not determined
Hosting location
Not determined
Not determined
Hosting options
Not determined
Not determined
Open source
Not determined
Not determined
Data processing agreement
Not determined
Not determined
Transfer impact assessment
Not determined
Not determined
Facts, side by side
Only facts both products carry under the same definition — anything else would not be a fair row.
Questions about Microsoft 365 Business and Proton for Business
Which is better, Microsoft 365 Business or Proton for Business?
As of 6 Nov 2026, the panel rates Proton for Business higher: 3.5/5 against 3/5. Weighted by what each judge cares about, 4 of the 6 judges pick Microsoft 365 Business and 2 pick Proton for Business. Which one fits depends on the criteria that matter to you; the table on this page shows both side by side, and each judge’s reading has its own page. Both were scored by the same AI bench under the same rubric, from public evidence only, as the methodology describes.
Is Microsoft 365 Business or Proton for Business European?
Microsoft 365 Business is not European by provenance (Rest of world). Proton for Business is European (UK / wider Europe). Provenance is read from each company’s own legal pages: who builds it and who owns it.