If an Exchange 2016 or 2019 is still sitting in your server cabinet, you probably did not open this article out of curiosity. On October 31, 2026, it is over — for good. The question that then lands in the ticket is always the same: “So what now?” Here are the four paths that remain, and the criteria we would use to decide ourselves. There is a recommendation at the end — after the comparison, not before it.
What happens on October 31, 2026
Regular support for Exchange Server 2016 and 2019 ended on October 14, 2025. Since then, security updates have only been available for money, as Extended Security Updates (ESU). The second and final ESU period ends on October 31, 2026; Microsoft rules out a third. After that, the same applies to everyone: no more patches, no matter how much you pay. If you never bought the ESU, you have been running unpatched since October 2025 anyway.
Why “just keep it running” is not an option: a mail server is, by definition, connected to the internet — port 25 for receiving, Outlook on the web (OWA) for the users. Every vulnerability that becomes known after the deadline stays open permanently. On October 28, 2025, the German BSI counted more than 30,000 German Exchange servers running discontinued versions with open OWA and calls continuing to run them negligent. A government agency rarely puts it more bluntly.
The successor, Exchange Server SE (Subscription Edition), is only available with subscription licenses. Buy once and run it for years is over — for a small company, a good reason to question its own Exchange altogether.
The four paths compared
| Operating model | Billing | Desktop Outlook | Data location | Who takes care of it | |
|---|---|---|---|---|---|
| Exchange Server SE | Your own server, run by you | Subscription licenses instead of purchase, plus hardware and admin time | Full Outlook in Exchange mode | On your premises | You or your IT provider |
| Microsoft 365 / Exchange Online | Microsoft cloud, your own tenant | Per user per month | Full Outlook in Exchange mode | Microsoft cloud (US provider) | Microsoft runs it, you manage the tenant |
| Hosted Exchange with a German provider | Exchange on the provider’s servers | Per mailbox per month | Full Outlook in Exchange mode | Germany, with the provider | Provider runs it, you click mailboxes |
| Your own open-source mail server (Mailcow-based) | Your own instance (self-run or hosted) or a shared server with the provider | Flat rate per plan or per server, not per head | IMAP/SMTP plus CalDav Synchronizer — no Exchange mode (MAPI) | Self-run: on your premises; hosted: with the provider — with us on our own hardware at three German locations | Self-run: you; hosted: the provider |
The first three paths are technically the same product — Exchange — in three places; what changes is the invoice, the location and who is responsible. The fourth is the only non-Exchange on the list, and therefore the only one where you have to reassess Outlook.
Five questions that decide
Do you absolutely need Outlook with Exchange comfort?
This is the question that beats all the others. Mailcow has no MAPI, so no modern desktop Outlook in Exchange mode. ActiveSync (EAS) no longer works with Outlook 2019 and newer, Microsoft 365 and the new Outlook — and SOGo, the groupware in Mailcow, is dropping ActiveSync entirely in 2026.
What works: Outlook on Windows via IMAP/SMTP, calendar and contacts through the free CalDav Synchronizer plugin. Fully covered: webmail (SOGo), iPhone and iPad with Apple Mail, Android, Thunderbird, Apple Mail on the Mac and eM Client.
What there isn’t: shared mailboxes in the Exchange sense, room booking, server-side Outlook rules as in Exchange. Server-side filters do exist — as Sieve filters in webmail, just not clicked together from inside Outlook.
If your team cannot work without these features: paths 1 to 3. If it lives on the smartphone, in the browser or in Thunderbird anyway, and Outlook is just “there”: path 4 is open. Which client fits where is covered in Which mail client fits you?.
How many mailboxes?
Billing per user is pleasant with three mailboxes and a budget line of its own with thirty. A flat rate works the other way round: within the tier, the eleventh mailbox costs nothing extra, and on an instance of your own the headcount does not matter at all. Do the math with your number; there is an example below.
Several domains?
Old company name, subsidiary, project domain — most companies have more than one. With our Mailhosting, it is one domain per plan; for the second you need a second package. A Mailcow instance of your own does not know this limit: one instance, all domains, all mailboxes underneath — with us as the Mail Server with its own sending IP.
Where should the data live?
With Exchange SE, on your premises. With Microsoft 365, in the Microsoft cloud. With hosted Exchange and hosted Mailcow, in Germany with the provider — with us on our own hardware at three German locations, data processing agreement under Art. 28 GDPR on request. Which location counts is decided by your customers, not by us.
Who administers?
Exchange SE needs someone who patches monthly, checks backups and renews certificates — permanently, not just during setup. Microsoft 365 needs a tenant admin who can find their way around Entra ID and licenses. Hosted Exchange and hosted Mailcow reduce that to creating mailboxes, setting passwords, maintaining aliases; the provider does the server part — with us, that is updates, backups, monitoring and a ticket answered by an engineer.
Worked example: 10 mailboxes
Prices including VAT, as of October 2026, as a rough order of magnitude with “around” — not a quote:
| Path | Per mailbox per month | 10 mailboxes per month | Per year |
|---|---|---|---|
| Microsoft 365 Business Basic | €7.22 | around €72 | around €870 |
| Exchange Online Plan 1 (Telekom) | €4.38 | around €44 | around €530 |
| Hosted Exchange with a German provider | around €10 | around €100 | around €1,200 |
| Exchange Server SE | Subscription instead of purchase, plus hardware, power, admin hours | cannot be quantified without a concrete quote | — |
| Your own Mailcow-based mail server | Flat rate per plan or server, no headcount | one plan, not ten invoice lines | — |
A note on fairness: Microsoft 365 Business Basic includes Teams, OneDrive and Office in the browser. If you only want to compare mail, take Exchange Online as the counterpart — hence the Telekom row. Our Mailhosting bills in mailbox tiers — one plan covers a fixed number of mailboxes, the plans are on the product page. What matters is the way of calculating: with the per-head models, every new mailbox costs exactly what is in the left column. From which number the flat rate wins, you can work out yourself in two minutes.
Our take
We run Mailcow ourselves for our Mailhosting and would rather not pretend it fits everyone. So, straight out:
Mailcow fits if your team reads mail in the browser, on the smartphone, in Thunderbird or Apple Mail. If you have several domains and want to pull them together on one instance. If data location Germany is an argument, not just a checkbox. And if you are tired of the per-head bill. A mail server of your own is then the alternative to Exchange Online or Microsoft 365 — with us as Mailhosting for one domain or as the Mail Server: your own Mailcow instance with its own sending IP for as many domains as you like.
Mailcow does not fit if your team needs Outlook in Exchange mode: shared mailboxes, room booking, server-side rules from inside Outlook. Then hosted Exchange with a German provider is the path that keeps Outlook and still gets the server out of your basement. We would rather say that before the order than in the ticket afterwards.
And because it often comes up in the same breath: Microsoft 365 is more than mail. Teams has no 1:1 replacement — Nextcloud Talk covers chat and video, with the Talk HPB for teams of up to 50 people, without Teams telephony and Teams apps. Nobody replaces Word, Excel and PowerPoint as desktop programs; Euro-Office in the browser, preinstalled in Nextcloud Hosting and Nextcloud Server, builds on the proven OnlyOffice engine and opens Office files with high compatibility. SharePoint workflows, Power Automate, Intune and Entra ID features are missing. The full picture, with the math, is in Replacing Microsoft 365.
Mail archiving is not part of the product, neither with Mailhosting nor with a Mailcow instance. If you need one, plan it separately.
Next steps
- Inventory. Mailboxes, distribution lists, functional addresses, domains, data volume per mailbox, clients in use. The typical surprise in migrations is mailboxes nobody had on the list anymore.
- Client check. Per user: which client, which platform? Which mail client fits you? answers that; for Outlook on Windows there is the setup via IMAP and CalDav Synchronizer.
- Migration in the right order. First synchronize mailboxes — via sync job in the Mailcow interface (imapsync), from Exchange via IMAP, as long as IMAP is enabled there; calendars and contacts via export from Outlook (ICS, vCard) and import into SOGo. Then switch MX, set SPF, DKIM and DMARC, then the remaining sync. Step by step: Migrating from Exchange to Mailcow; whether SPF, DKIM and DMARC pass, you check with a test mail after the first login as domain admin.
- Build reputation. A new sending environment has no history. No bulk mail in the first weeks; the levers are in Building mail reputation.
- Not sure which path? Open a ticket with mailbox count, domains and client list. We will tell you whether Mailcow fits — and if not, we will say that too.
Frequently asked questions
Can I keep Exchange 2016/2019 running behind the firewall after October 31, 2026? A mail server that receives mail is reachable from the internet — otherwise it receives nothing. After the deadline, every newly discovered vulnerability stays open permanently. The BSI calls continuing to run it negligent; we have nothing to add.
Does Outlook work with a Mailcow server? On Windows, yes — via IMAP/SMTP, calendar and contacts through CalDav Synchronizer. What doesn’t work: Exchange mode (MAPI) and ActiveSync with Outlook 2019 and newer, Microsoft 365 or the new Outlook. The new Outlook additionally routes IMAP accounts through Microsoft servers; what that means for you is in Setting up the Windows Mail app and the new Outlook.
What becomes of shared mailboxes, room booking and Outlook rules?
Functional addresses like info@ you set up as an alias to several recipients or as a regular mailbox with shared access — a shared-mailbox concept as in Exchange it is not. Room booking does not exist. Rules you create server-side as Sieve filters in webmail, not in Outlook.
Can the migration run directly out of Exchange? Yes, via IMAP, as long as IMAP is enabled on the Exchange; the sync job runs in the Mailcow interface. If the data only exists as PST, you drag and drop it into the IMAP account in Outlook — or we take over the migration as the assisted variant, via ticket.
Can I move mail first and decide on Microsoft 365 later? Yes. Mail hangs on your MX record, not on Teams or Office. You can bring mail to us and leave Teams, OneDrive or the desktop Office programs with Microsoft until the rest is decided.
What’s next
First login as domain admin in the Mailcow GUI
After ordering your mail server plan, you get access to the Mailcow GUI. Here's an overview of what you see as domain admin and where to find what.
Creating and editing mailboxes, setting quotas
How to create new mail addresses as domain admin, assign storage quotas, change passwords and delete mailboxes again.
Setting up aliases and a catchall
Route several mail addresses into one mailbox — info@, kontakt@, presse@ all in a single inbox. Plus a catchall for every typo address.
Creating app passwords for mail clients
With 2FA active, Outlook, Apple Mail and friends need an app password instead of your main password. How to create them, revoke them and avoid password chaos.