Replacing Microsoft 365: what Mailcow and Nextcloud can do — and what they cannot

For many companies, Microsoft 365 is the operating system of the office: mail, calendar, files, office, Teams — one subscription, everything included. In 2026, noticeably more businesses are asking us how much of that can be mapped onto Mailcow and Nextcloud. The short answer: most of it, but not all. Below, block by block: what works, what works with limitations, and what has no replacement.

Why so many are thinking about it in 2026

Three reasons come up in tickets again and again.

The price per user. Microsoft 365 Business Basic costs around €7 per user per month (as of October 2026: €7.22 including VAT). For ten people that is around €72 a month, for 25 around €180 — and every new colleague costs the full rate. Our Nextcloud Server is billed by storage, not per head; Mailhosting by mailbox package.

The Exchange in the server cabinet. Exchange Server 2016 and 2019 have been out of regular support since October 14, 2025. The paid Extended Security Updates (ESU) end on October 31, 2026, and Microsoft rules out a third period. The successor, Exchange Server SE, is only available with subscription licenses. On October 28, 2025, the German BSI counted more than 30,000 German Exchange servers running discontinued versions with open web access (OWA) and calls continuing to run them negligent. If you have a server like that, you have to move anyway — the only question is where.

Data location and dependency. With Microsoft 365, mails and files sit with a US vendor, which sets the price and the feature set. With us, the data sits on our own hardware at three German locations, and you can cancel, export or move mail and cloud separately. That is not a moral argument but a business one: one supplier fewer that everything depends on.

Block by block

Microsoft 365	Counterpart with us	Status
Exchange Online (mail, calendar, contacts)	Mailcow with SOGo — Mailhosting with your own domain or Postfach without one	with limitations: no Exchange mode for desktop Outlook
OneDrive, SharePoint files	Nextcloud Hosting or Nextcloud Server: desktop sync, shares, version history	complete
Word, Excel, PowerPoint in the browser	Euro-Office, preinstalled in both Nextcloud products	complete
Word, Excel, PowerPoint as desktop programs	no replacement — desktop Office stays, the files live in Nextcloud	no replacement
Teams: chat and video	Nextcloud Talk; with Talk HPB up to 50 concurrent users, recording as an add-on	with limitations
Teams: telephony, Teams apps	—	no replacement
Planner, To Do	Nextcloud Deck (Kanban) and Tasks	complete
OneNote	Nextcloud Notes (Markdown notes)	with limitations
Microsoft Whiteboard	Nextcloud Whiteboard — active out of the box on Nextcloud Server	complete (Server)
SharePoint workflows, Power Automate	—	no replacement
Intune, Entra ID	—	no replacement

The most important rows in detail:

Mail. Mailcow delivers mail via IMAP/SMTP, calendar and contacts via CalDAV/CardDAV, plus SOGo as webmail with calendar, address book and tasks. Fully covered: webmail, iPhone and iPad with Apple Mail, Android, Thunderbird, Apple Mail on the Mac and eM Client. Outlook on Windows works via IMAP plus the CalDav Synchronizer plugin for calendar and contacts — it works, but not in Exchange mode. Which app fits whom is covered in Which mail client fits you?.

Files. The Nextcloud desktop client replaces the OneDrive folder, internal and link shares replace the SharePoint library for small teams, and version history is included. Start here: Desktop client and Sharing internally and externally.

Office. Euro-Office is the sovereign office suite from Europe, backed among others by Nextcloud, IONOS, XWiki and OpenProject. It builds on the proven OnlyOffice engine and opens and edits .docx, .xlsx and .pptx with high compatibility to Microsoft Office — several people at once, in the browser. What it is not: a replacement for installed desktop Office with macros and add-ins. Details in Office in Nextcloud.

Chat and video. Talk covers group chats, calls, screen sharing and guests via link. For calls beyond a handful of participants, the High Performance Backend is part of the setup (up to 50 concurrent Talk users); recordings run through a separate backend. What Talk cannot do is covered in Talk — chat and video conferencing.

Three businesses, three answers

Trade business, 8 people — a fit. Two office workstations, everyone else reads mail on a smartphone. Quotes and invoices as files, a shared calendar for the job sites, a chat for the fitters. Mail via Mailhosting, files and calendar in Nextcloud, documents in Euro-Office in the browser — nobody in the business needs desktop Outlook. At around €7 per user, that is around €58 a month that no longer goes to Microsoft. What you pay us instead is on the product pages.

Agency, 15 people, desktop Office mandatory — a partial fit. Clients send Word documents with tracked changes and Excel models with macros; the agency delivers PowerPoint in corporate design. Files and mail move to us, Teams is replaced by Talk with HPB. Desktop Office stays installed and works on the files in the Nextcloud folder; Euro-Office in the browser is the supplement for quick edits, not the replacement. Part of the license cost remains; in return, mails and files are no longer billed per head with a US vendor. Anyone used to the Exchange comfort in Outlook has to want the switch to IMAP plus plugin — settle that with the team beforehand, not afterwards.

Company with Teams telephony and Power Automate workflows — not a fit. The phone system runs in Teams, incoming invoices travel through SharePoint via Power Automate, the notebooks are enrolled in Intune. We have no replacement for that, and we are not going to build one. At most, a partial move is worth it here — say, the file archive to Nextcloud — and the rest stays. We would rather say that before the order than in the first ticket.

Order of the switch

Our rule of thumb: files first, mail after. Files can run in parallel for weeks without anyone noticing; mail has a cutover date with a DNS switch. One exception: if an unpatched Exchange is running in-house, mail moves to the front.

1. Inventory. Which Microsoft 365 features does your team actually use? Teams telephony, Power Automate flows, shared mailboxes, room booking, Intune — every hit is either a “no replacement” from the table or an item for the plan.
2. Set up Nextcloud. Create users and groups (Users and groups), carry over the folder structure from SharePoint and OneDrive, upload files via the desktop client, set the shares up again. Then work with real documents in Euro-Office for two weeks before anyone switches off OneDrive.
3. Create mailboxes and synchronize. Create the mailboxes in Mailcow and start the sync job in the Mailcow interface — it fetches all mails, folders and read status via IMAP in the background. From an in-house Exchange this works the same way, as long as IMAP is enabled on the Exchange. You export calendars as ICS, contacts as vCard or from Outlook, and import both into SOGo. PST files you drag and drop into the IMAP account in Outlook — or you hand the migration to us as the assisted variant via ticket. Step by step: Migrating from Microsoft 365.
4. Switch DNS. Only once the first sync is through: point MX to our servers, set SPF, DKIM and DMARC, then one last differential sync. The domain then needs four to eight weeks of warm-up — how that works is in Building mail reputation.
5. Switch clients. Smartphones and desktops to IMAP/CalDAV/CardDAV, with the credentials from the server details reference; Nextcloud apps on desktop and mobile devices.
6. Run in parallel, then cancel. Keep both sides open for two weeks, then let the Microsoft licenses expire.

Straight talk: what doesn’t work

• No Exchange mode for desktop Outlook. Mailcow does not speak MAPI. ActiveSync (EAS) no longer works with Outlook 2019 and newer, Microsoft 365 and the new Outlook, and SOGo is dropping ActiveSync entirely in 2026. Outlook on Windows works via IMAP/SMTP plus CalDav Synchronizer; instructions in Setting up Outlook on Windows.
• No shared mailboxes in the Exchange sense. Shared addresses are handled via aliases or a separate mailbox with its own password — see Aliases and catchall. Room booking as in Exchange and server-side Outlook rules do not exist; server-side filters exist as Sieve.
• No mail archiving. If you have to archive emails under statutory retention periods, you need a separate tool for that. It is not part of our mail products.
• One domain per Mailhosting plan. Several company names means with Mailhosting: one package per domain. For several domains on one instance there is the Mail Server — your own Mailcow instance with its own sending IP, unlimited domains and mailboxes.
• No desktop Office, no Teams telephony, no workflows. Word, Excel and PowerPoint as installed programs, Teams telephony and Teams apps, Power Automate, Intune and Entra ID have no counterpart with us.

Frequently asked questions

Can our people keep using Outlook? Yes, via IMAP/SMTP; calendar and contacts come via the free CalDav Synchronizer plugin. What doesn’t work: Exchange mode with server rules, shared mailboxes and room booking. If you need exactly that, a hosted Exchange offer (around €10 per mailbox) is a better home than we are.

Do we have to move mail and files together? No. Nextcloud works regardless of where your mail lives. Many companies move the files first, keep Exchange Online for another year and bring the mail over later — or the other way round.

What does it cost with you? Microsoft 365 Business Basic is around €7 per user per month. Our prices are on the product pages for Mailhosting, Nextcloud Hosting and Nextcloud Server; Nextcloud Server is billed by storage, not by users. Do the math with your headcount.

How do we invite external people to video calls? Via link. Talk generates a guest link for every conversation; the guest only needs a browser. For calls beyond a handful of participants, the HPB is part of the setup.

How long does a complete switch take? Files: a few days depending on volume, plus two weeks running in parallel. Mail: one day for small setups, two to four days for 25 mailboxes — details in Migrating from Microsoft 365. Add the mail reputation warm-up on top.

Who helps if we are not sure? Open a ticket with your headcount, the Microsoft 365 features you use and whether desktop Outlook is mandatory. One of the three of us replies with an assessment — even if it is a “no”.