The open-source alternative to Microsoft, Google & more
Email, calendar, chat, files and video on one sovereign, open-source platform — with native Outlook support and open standards. Compare features and total cost of ownership against Microsoft, Google and the alternatives, and keep full control of your data.
Compare the cost of grommunio
Compare grommunio against on-premises Microsoft Exchange and other self-hosted platforms, or the Microsoft 365 and Google Workspace clouds. Every figure is an editable estimate — adjust them to match your environment.
Cost scope
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Every figure is an editable estimate. Cloud prices shown here are public list prices (Austria, ex VAT); on-premises licensing for the other platforms is typically not publicly listed — confirm rates with the vendor or your reseller.
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Enterprise
Let's talk volume pricing
Above 1,000 mailboxes, pricing is tailored to your deployment. Tell us your numbers and we'll put together an offer.
Heads up — these are illustrative estimates based on public list prices and typical assumptions, not a quote. Sector-specific discounts (for example educational or governmental rates) available from grommunio or any competitor are not reflected here, and negotiated or volume-specific pricing can't simply be applied either. For an accurate, tailored offer, talk to us or a certified partner.
A direct replacement, not a full rebuild
grommunio implements open and Exchange-compatible standards, so your users and clients carry on as before — while you keep control of cost, data and infrastructure.
- Keep Outlook — no plugins Outlook for Windows connects natively over MAPI/HTTP, exactly as it does to Exchange. Nothing to install on the client, no connectors in between.
- Every client connects EWS, Exchange ActiveSync, IMAP/POP3/SMTP and CalDAV/CardDAV — Apple Mail, Thunderbird, eM Client, iOS and Android all work out of the box.
- About half the resources The lightweight C/C++ gromox core needs roughly half the infrastructure of Microsoft Exchange Server SE for the same number of mailboxes.
- One simple subscription One transparent per-user subscription that includes the whole platform — no Client Access Licenses, no Software Assurance, no per-seat cloud tiers.
- Your data, your jurisdiction Self-host on-premises, in your private cloud, or with a certified European partner — full data sovereignty, no vendor lock-in.
- Open Source & auditable 100% open source on GitHub and Codeberg. Inspect it, integrate with it, and leave whenever you want — there's nothing to be locked into.
How grommunio compares
Mail and collaboration platforms differ in far more than price. Here's how grommunio lines up against the main alternatives — including sovereign suites like openDesk — and the few places where it deliberately doesn't compete, such as bundling Microsoft Office licenses. Hover or tap any marked cell for the detail.
| Capability | grommunio | Microsoft Exchange | Microsoft 365 | Google Workspace | Kerio Connect | Zimbra | Open-Xchange | openDesk |
|---|---|---|---|---|---|---|---|---|
| Outlook & client access | ||||||||
| Native Outlook via MAPI/HTTP The Outlook your users already have — no connector or add-in to install on each PC. | ||||||||
| Exchange ActiveSync (mobile push) Push mail, calendar and contacts to phones and tablets out of the box. | ||||||||
| Exchange Web Services (EWS) The API many Mac, mobile and third-party mail clients rely on. | ||||||||
| IMAP, POP3 & SMTP Universal open mail protocols, supported by every client. | ||||||||
| CalDAV & CardDAV Open calendar and contact sync — Apple, Thunderbird, mobile, anything standards-based. | ||||||||
| Modern web client (mail, calendar, contacts) A full-featured browser client — no desktop install required. | ||||||||
| Autodiscover / autoconfig Clients configure themselves from just an email address. | ||||||||
| Groupware & Exchange parity | ||||||||
| Offline Address Book (OAB) A cached global address list available to desktop clients while offline. | ||||||||
| Shared mailboxes over Exchange ActiveSync Reach a shared mailbox from a phone over EAS — via grommunio's EAS impersonation. | ||||||||
| Delegation, Send-As & Send-on-Behalf Let assistants manage and send mail on a manager's behalf, the Exchange way. | ||||||||
| Tasks & Notes Dedicated Tasks and Notes apps, synced like mail and calendar. | ||||||||
| Public folders (Exchange-style) Genuine MAPI public folders shared across the organisation — not just shared user folders. | ||||||||
| PST / OST import tooling Vendor-supplied tools to import Outlook PST/OST archives or migrate from Exchange. | ||||||||
| Collaboration & productivity | ||||||||
| Built-in chat & messaging Team chat as part of the platform, not a separate purchase. | ||||||||
| Built-in video meetings Browser-based video conferencing included with the platform. | ||||||||
| File sharing & storage Personal and shared file storage with links and sync. | ||||||||
| Online document editing Edit documents and spreadsheets in the browser. | ||||||||
| Microsoft Office desktop apps Word, Excel and PowerPoint desktop licenses bundled with the subscription — grommunio does not include these. | ||||||||
| Deployment & sovereignty | ||||||||
| Self-hosted / on-premises Run it entirely on your own infrastructure. | ||||||||
| Runs on Linux No Windows Server licenses required underneath. | ||||||||
| Runs without Microsoft AD / Entra ID No hard dependency on a Microsoft directory. | ||||||||
| Multiple LDAP/AD backends per install Attach several independent directories to one installation — ideal for multi-tenant hosting. | ||||||||
| European vendor (data sovereignty) Vendor jurisdiction — who ultimately controls the software and its roadmap. | ||||||||
| Declarative / Infrastructure-as-Code config Manage configuration from version-controlled state (Ansible, Puppet, Terraform, Helm, DSC). | ||||||||
| Ready-to-run appliance / VM image Boot a preconfigured ISO, OVA or container image — no manual stack assembly. | ||||||||
| Runs on common hypervisors and containers VMware, Hyper-V, Proxmox / KVM, Xen / XCP-ng, plus Docker and Kubernetes. | ||||||||
| Openness & licensing | ||||||||
| OSI-approved open source Source available under an OSI-approved license you can audit and self-host. | ||||||||
| Free, fully-featured community edition A genuinely free edition with the full feature set. | ||||||||
| Transparent public per-user pricing A published price you can read without a sales call. | ||||||||
| Security & administration | ||||||||
| S/MIME email encryption End-to-end message signing and encryption. | ||||||||
| Single sign-on (SAML / OIDC) Log in through your own identity provider. | ||||||||
| Mobile device management Device policies and remote wipe for phones and tablets. | ||||||||
| Multi-tenancy (host multiple organizations) Serve many isolated organizations from one deployment. | ||||||||
| Multi-factor authentication (MFA) Two-factor / multi-factor sign-in for webmail and admin — TOTP, FIDO2 or via your IdP. | ||||||||
| Built-in antispam & malware defense Spam filtering and malware scanning included with the platform, not an extra product. | ||||||||
| Administration & automation | ||||||||
| Unified web admin console One console to manage users, domains and the whole platform. | ||||||||
| Scriptable REST admin API Provision and manage programmatically over a documented API. | ||||||||
| Command-line administration Drive the server from the shell for automation and bulk operations. | ||||||||
| PowerShell management A native PowerShell interface for Windows-centric administrators. | ||||||||
- Capabilities verified against each vendor’s own documentation. Items that depend on a paid edition, a separate add-on or a desktop connector are marked accordingly rather than as a plain “included”.
- grommunio is open source: every feature ships in every edition, including the free Community edition. Paid subscriptions add manufacturer support — collaboration apps (Chat, Meet) are supported from the Plus tier, and Files, Office, archiving and device management from Business. Cost figures above use the Business tier for a fair, fully-supported like-for-like.
We let the product speak for itself
grommunio does not appear in the EU Transparency Register and runs no lobbying operation — we would rather put our energy into the product than into political influence. For comparison, the register lists Microsoft at roughly €7 million a year and Google at around €4.5 million, and Open-Xchange has been registered since 2017. We think software should win on its merits. Source: EU Transparency Register.
Switch to grommunio
Is grommunio a drop-in replacement for Exchange?
Yes. grommunio implements the native Exchange protocols — MAPI/HTTP, EWS and Exchange ActiveSync — so Outlook for Windows and other Exchange clients connect natively, without plugins or connectors. For most organizations it's a server-side switch, not a client rollout.
Do our users have to give up Outlook?
No. Outlook for Windows works natively over MAPI/HTTP, and Outlook for Mac via EWS. Your users keep the client they know; only the backend changes.
How does grommunio compare on cost to Microsoft, Google, Kerio or Zimbra?
grommunio is one transparent per-user subscription that includes the whole platform, and you can self-host on infrastructure you already run — so there's no per-seat cloud tier and no licensing stack to maintain. Use the calculator above to compare your own numbers against Microsoft Exchange, Microsoft 365, Google Workspace, Kerio Connect or Zimbra.
What about Exchange CALs and Software Assurance?
Not needed. grommunio is licensed as a simple per-user subscription via certified partners. There are no Client Access Licenses, no Windows Server CALs, and no mandatory Software Assurance to maintain.
Is it true grommunio needs about half the resources of Exchange?
Yes — the gromox core is a lightweight, Linux-native C/C++ engine. For a comparable number of mailboxes it typically requires roughly half the server resources of Microsoft Exchange Server SE, which is reflected in the fully-loaded TCO above.
How hard is the migration itself?
grommunio provides migration tooling and a network of certified partners to plan and execute the move from Microsoft or Google, including importing existing mailboxes. Talk to us and we'll connect you with a partner in your region.
Legal Notice: grommunio is an independent software product and is not affiliated with, endorsed by, or sponsored by Microsoft, Google, Amazon, GFI, Synacor, Open-Xchange, ZenDiS or any other third party. All product names, logos, brands and trademarks — including Microsoft 365, Microsoft Exchange, Microsoft Outlook, Google Workspace, Kerio Connect, Zimbra, Open-Xchange and openDesk — are the property of their respective owners and are used solely for identification, comparison and contextual purposes. Their use does not imply any endorsement or affiliation.