Backup you can prove is restorable.
Open-source, self-hosted backup for Microsoft 365 and IMAP. Every backup is read back through the restore path and compared byte for byte before Osiris calls it restorable.
restore check: weekly, per mailbox and OneDrive
sample: ≈20 mails, 20 files, calendar, contacts
method: read back, compared byte for byte
shown as: recovery readiness on the dashboard
Osiris 0.303.0, unretouched screenshot with synthetic sample data.Nothing here is a mockup.
Back up, verify, restore. In that order, every week.
Back up
Exchange Online mail, calendar, contacts and OneDrive through the Graph API, IMAP mailboxes over IMAP. Incremental, deduplicated, encrypted, on your storage.
Verify
A weekly job reads a sample from each latest snapshot back through the restore path and compares hashes. A backup that was never checked is never shown as proven.
Restore
A single message, a folder, an older file version or a whole mailbox, into the original account or another one. The same path an emergency restore uses.
Restore is non-destructive by default: recovered items go next to what is already there, never over it. Removing the beta's remaining ‘Replace’ mode is in progress.
What the product looks like
Unretouched screenshots of Osiris 0.303.0 from the public demo with synthetic tenants.
What it protects, and what is still being built
Backup
- Exchange Online: mail, calendar, contacts
- OneDrive
- IMAP mailboxes
- Non-destructive restore, every restore logged
- Weekly sampled restore checks
Archive and organisation
- Archive on Exchange Online journaling, built for German GoBD requirements
- Hash-chained, object-lock immutability where storage supports it
- Single sign-on, roles and four-eyes approval
- Signed restore report
Servers and virtual machines
- Linux and Windows server and client agent
- Proxmox VE via Proxmox Backup Server
- SFTP storage target, arm64 images
Stated limits: Teams messages are not part of v1. An IMAP source currently uses one login for all mailboxes under it. The first backup of a large tenant can take days, because Microsoft throttles the Graph API; Osiris shows that wait instead of hiding it.
Editions
Everything you need to back up is free. Everything your organisation needs to sign off on is Business.
Early access. Osiris is in closed beta. Business and Service Provider licences are sold now at 30% off. You get the licence for good and every feature the edition adds during the beta, as it ships. Today, Service Provider already unlocks multiple tenants and the cross-tenant API; Business currently adds nothing beyond Community. No dates are promised. Not to be used as your only backup.
Community
Free
One organisation. Every backup source, every restore function, no mailbox limit, no licence key.
- Microsoft 365 and IMAP backup
- Non-destructive restore
- Weekly restore checks
- Audit log, REST API
For homelabs, small teams and anyone who wants to see the code.
Business
List price€250 Early access price€175once, net, plus VAT
Everything in Community, plus what an organisation needs to prove.
- Single sign-on (Entra ID, OIDC, LDAP)
- Roles and four-eyes approval
- Archive built for German GoBD requirements
- Signed, verifiable restore report
For one company. Business customers only (§ 14 BGB). SSO, roles, archive and the restore report are in development, not available yet.
Service Provider
List price€950 Early access price€665once, net, plus VAT
Everything in Business, plus running Osiris for many clients.
- Multiple tenants
- Delegated tenant administrators, tenant reporting
- Cross-tenant REST API for RMM and PSA
- White label
For IT service providers. Business customers only (§ 14 BGB). Multiple tenants and the cross-tenant API are available today; delegated administrators, tenant reporting and white label are in development.
| Included | Community | Business | Service Provider |
|---|---|---|---|
| Available now | |||
| Tenants | One | One | Multiple |
| REST API | Yes | Yes | Yes, plus a cross-tenant provider key |
| In development | |||
| Single sign-on (Entra ID, OIDC, LDAP) | No | Planned | Planned |
| Roles and permissions, four-eyes approval | No | Planned | Planned |
| Archive layer for German GoBD requirements | No | Planned | Planned |
| Signed, independently verifiable restore report | No | Planned | Planned |
| Delegated tenant administrators, tenant reporting | No | No | Planned |
| White label | No | No | Planned |
One-time purchase. A signed key, verified offline. No phone-home, nothing that can switch the software off, no subscription that lapses.
All updates included. For as long as we actively develop Osiris. If we ever stop, we announce it twelve months in advance and publish the Business and Service Provider modules under the AGPL. Your installation keeps running without a key.
Software only. Licences include the software and all updates. No support is included.
Honour rule. Mailbox and tenant counts are not enforced technically. We trust you to buy the edition that matches how you use Osiris.
Full pricing and terms · How Osiris compares with eight other vendors
Your data is your data
Encrypted before it leaves the server
AES-256-GCM per chunk, a separate key per organisation.
Storage you choose
Local disk, S3-compatible object storage, NFS or SMB. More than one target per organisation.
An open, documented format
A small standalone tool restores from it even without a running Osiris server. Losing Osiris does not mean losing your backups.
No phone-home
No telemetry, no licence server, no connection to us. Osiris only talks to what you configure.
Source code on GitHub · How Osiris is built, loop by loop
Who runs it
Run it yourself
A Docker Compose stack on a server you control. How Community and Business are normally used.
Have your IT service provider run it
Your provider installs and operates Osiris for you, on their infrastructure or yours, under the Service Provider edition. Osiris itself does not offer a hosted service.
About the project
Osiris is built by Lucas Flores, an IT systems engineer and owner of a small managed service provider near Cologne, not a professional software developer. The code is written with AI assistance, with his own understanding of Exchange, Graph and storage, and a testing discipline that is not negotiable for a backup tool. If you consider that a risk, you are right to; that is why the tests, the restore evidence and the storage format stay open.
Lucas Flores, IT Systeme Flores UG · last updated 2026-09-24
Get Osiris Community
Community is free and open source, licensed under the AGPL-3.0.
Get started
Osiris is currently in closed beta; the first public release will be version 0.1.0. Until then, build and run it from source with Docker Compose.
Business and Service Provider editions unlock in the same installation with a licence key: no separate download, no separate signup.
Get notified when the beta opens
Nothing to buy and no account to create. We email you once, when your edition or the live demo is ready.
Questions
What happens if Osiris development ever stops?
We announce it at least twelve months in advance and publish the Business and Service Provider modules under the AGPL. Your installation keeps running without a licence key, and the AGPL core already released cannot be withdrawn.
Where is my data stored?
Wherever you point Osiris: local storage, S3-compatible object storage, NFS or SMB. If your IT service provider runs Osiris for you, they tell you where. Osiris itself never stores your data on our infrastructure.
What Microsoft 365 permissions does Osiris need?
An Entra ID app registration that your tenant administrator consents to once, with Graph application permissions scoped to backup and restore. Osiris only uses Graph, never EWS and never legacy authentication. The exact list is in the documentation.
Is the archive available yet?
No. Journaling, retention, legal hold and end-user archive search are in development. Backup for Exchange Online, OneDrive and IMAP is what the closed beta covers today.
Is Osiris open source?
The core (backup, restore, audit log) is AGPL-3.0 with a plugin exception and will be published on GitHub with the first public release. Business and Service Provider add proprietary modules unlocked by a licence key.
Can I try a live demo?
Not publicly yet. A demo with a synthetic mailbox is planned for the next release. Leave your address above and we tell you the moment it is reachable.