Zimbra FOSS vs Microsoft 365 — a real comparison of cost, features and data control. When a self-hosted server saves thousands and when 365 is the better choice…
What you get with Zimbra on your own server and what you miss from Microsoft 365 — a real comparison without marketing, with concrete numbers and practical considerations.
Microsoft 365 Business Basic
15 users × €6/month = €90/month
12 months = €1,080/year
5 years = €5,400
Zimbra on own server
One-time setup + hardware
Monthly cost ≈ €0 (own server)
5 years = ~€500 (electricity + domain)We install and configure Zimbra for your organisation — with all domains, SPF, DKIM, DMARC and SSL.
Zimbra is a full-featured email and collaboration platform — webmail, calendar, contacts, tasks, shared folders. It runs on your own server, under your control. Your data stays with you, not in Microsoft's cloud.
It has existed since 2005 and is used by universities, government organisations and companies worldwide. The FOSS edition is completely free — no monthly subscription, no user limits, no expiring licences.
| Feature | Zimbra (own server) | Microsoft 365 Business Basic |
|---|---|---|
| Email (IMAP/SMTP) | ✅ Yes | ✅ Yes |
| Webmail | ✅ Zimbra Web Client | ✅ Outlook Web |
| Calendar | ✅ Yes | ✅ Yes |
| Contacts | ✅ Yes | ✅ Yes |
| Mobile sync | ✅ ActiveSync | ✅ Yes |
| Outlook connector | ✅ Zimbra Connector for Outlook | ✅ Native |
| Anti-spam and antivirus | ✅ Amavis + ClamAV included | ✅ Defender included |
| Word, Excel, PowerPoint online | ❌ No | ✅ Included |
| SharePoint / Teams | ❌ No | ✅ Yes |
| OneDrive (1TB) | ❌ No | ✅ Yes |
| Multiple domains | ✅ Unlimited | ❌ Paid add-on |
| Data stays with you | ✅ On your server | ❌ Microsoft cloud |
| Cost (10 users/month) | ~€0 | €60 |
Agencies, hosting companies, organisations with multiple brands — one server, unlimited domains, no extra cost per domain.
Lawyers, accountants, medical practices — confidential correspondence that must not sit in someone else's cloud.
Organisations with 10+ users where Microsoft 365 costs grow quickly and exceed the investment in a self-hosted server.
If you want your own mail server with full control and no monthly fees:
Yes. Zimbra supports standard IMAP/SMTP protocols, so any email client works. There is also a dedicated Zimbra Connector for Outlook that adds calendar and contacts synchronisation.
Emails sent to you while the server is down are held by the sending server and delivered when yours recovers — typically up to 5 days. With 24/7 monitoring we react before there is a real problem.
Zimbra FOSS has no user limit. For most small and medium organisations it is more than sufficient.
Zimbra allows viewing attached Office files. For editing you need LibreOffice locally, or you can integrate Nextcloud with OnlyOffice for online editing directly in the browser.
A properly configured server with up-to-date software and regular updates is as secure as any cloud service. The advantage is full control — you know exactly what happens with your data.
Yes. The process involves exporting existing mail and transferring it via IMAP synchronisation. The migration itself typically takes hours, not days. Contact us for details.
This article was written after a real installation and configuration of Zimbra FOSS 10.1.16 on Ubuntu 22.04 with multiple domains, Let's Encrypt SSL, SPF, DKIM and DMARC. We do the same for clients — because a self-hosted mail server is a realistic alternative, not just theory.