Synology Active Backup for Microsoft 365 alternative and comparison 2026
Active Backup for Microsoft 365 is a free add-on for Synology NAS devices. There is no license and no account limit; you need a Synology NAS with enough storage. It is the most common self-hosted Microsoft 365 backup in small businesses and homelabs.
By Lucas Flores, IT Systeme Flores UG. Last updated
Synology product page and DSM 7.3 technical specifications checked on 2026-09-29. The EWS and Microsoft Graph details were read in Synology's knowledge base on 2026-10-22.
The short answer
Synology fits if you already own a Synology NAS: Microsoft 365 backup costs nothing extra, covers SharePoint and Teams, and exports to PST, ICS and CSV.
Restow fits if you want the same self-hosted idea without being tied to one hardware brand, plus a weekly restore test, IMAP mailboxes and, for MSPs, many tenants in one installation. Restow Community is free as well.
At a glance
| Aspect | Restow | Synology |
|---|---|---|
| Price model | Community free. Business €595, Service Provider €1,950, one-time, net (pre-sale until release: €476 and €1,560). Pre-sale licenses include every 1.x update; from version 1.0, a license includes 12 months of updates, then an optional update year (Business €295, Service Provider €595 net per year). No per-user fee. | Free add-on, no license, unlimited accounts. Requires a Synology NAS. |
| Where it runs | Self-hosted: one Docker Compose stack on a Linux server or VM you control. | On a Synology NAS with DSM. |
| Where backups are stored | Your choice: local disk, S3-compatible object storage or NFS, in the region you pick. Immutable backups (S3 Object Lock) can be switched on per repository. | The NAS itself. |
| Microsoft 365 coverage | Exchange Online mail, calendar, contacts; OneDrive; SharePoint Online sites (document libraries and lists, new in 0.4.0); Microsoft 365 groups (calendar and conversations, opt-in, since 0.4.5); IMAP mailboxes; Linux and macOS servers and clients (file-level agent); SMB and NFS file shares without an agent; imported mail files. No Teams chats. | Exchange mail, contacts, calendars; OneDrive; SharePoint libraries and lists; Teams posts. |
| Restore testing | Weekly sampled check: data is read back through the restore path and verified against the recorded hashes. File shares are checked after every new restore point, Proxmox VE (preview) guests within minutes of every new restore point, and Proxmox VE can also boot-test restore points. | Not described on the pages checked. |
| Source code and exit | Apache 2.0 core, Business and Service Provider modules under the Restow license terms, open documented storage format with a standalone restore tool. | Proprietary, internal format not open. Exports to EML, PST, CSV, ICS and HTML. |
Where Synology is strong
- No license cost at all on existing Synology hardware.
- Covers SharePoint and Teams.
- Continuous, scheduled or manual backup, unlimited recovery points.
- Exports mail to PST and EML.
Where Restow is different
- Runs on any Linux server or VM, not only on one vendor's NAS.
- Writes to local disk, S3-compatible object storage or NFS, so an off-site copy is easy.
- A weekly restore test per mailbox that reads data back and compares it.
- IMAP mailboxes too, and multiple tenants for service providers (Service Provider edition).
- Open source core and an open storage format with a standalone restore tool.
EWS retirement and Active Backup
Microsoft is switching off Exchange Web Services (EWS) in Exchange Online in phases; our guide to the EWS retirement has the dates. Synology's knowledge base says Active Backup for Microsoft 365 moved the services that Microsoft Graph supports to Graph in version 3.0.0, and that mail restores now use Graph and need the permission MailboxItem.ImportExport.All. Backup and restore of archive mailboxes, group mail and group calendars, and of services hosted in the China region, still use EWS, because Graph does not support those scenarios yet. For those parts an administrator has to keep EWS enabled and add the app to the tenant's EWS allow list. Synology writes that it plans to move the remaining services to Graph if Microsoft adds the missing support, and that it may discontinue backup support for them if it does not; Microsoft discontinues EWS on 1 April 2027.
Restow has never used EWS. It reads Exchange Online mail, calendar and contacts, OneDrive and SharePoint sites through Microsoft Graph only, so there is nothing to allow-list. Exchange public folders and Teams chats are outside its scope.
What Restow does not do (yet)
- Restow does not back up Teams chats. It backs up SharePoint Online sites since 0.4.0, without attachments of list items, site design, navigation and workflows; permissions are kept as information and never restored.
- Immutable backups (new in 0.4.0) are off until an administrator turns them on per repository. S3 Object Lock was tested against a simulated S3 service only, directories and NFS get only a deletion delay, which is not immutability, and the installation's default repository cannot be made immutable.
- In Business, the audit log viewer ships since 0.1.0 and the audit log export since 0.3.1; since 0.3.1 every edition has several administrators with roles. Sign-in with Microsoft and single sign-on (SSO) are planned, and so are four-eyes approval and a signed restore proof.
- The archive is filled by mail import with archiving and, from Business, by capture from the mailboxes (Microsoft Graph, IMAP sync), Exchange Online journal receipt and forwarded copies. Capture from the mailbox is near-time and not complete, and was tested against simulated services only.
- The automated Microsoft 365 backup and restore check against a real tenant is not active yet: check 4 of the release pipeline was skipped in every release so far; Microsoft 365 is covered by tests against a simulated Graph API.
- Licenses include no support, setup, operation or SLA.
- The server and endpoint agent runs on Linux and macOS, file-level; a Windows agent and image backup are planned.
- Restow is a beta: do not use it as your only backup.
Synology: the facts, with sources
Each line is taken from Synology's own documentation unless the rating says otherwise. "Checked: not found" means we looked in the named sources and did not find it, which is not proof that it does not exist.
| Fact | Source | How solid |
|---|---|---|
| Active Backup for Microsoft 365 is a free add-on for Synology NAS servers; no licenses are required and the number of accounts is unlimited, as far as storage allows. | Synology: Active Backup for Microsoft 365 | Official source |
| Runs only on a Synology NAS with DSM; deduplication needs an x64 model with the Btrfs file system. | Synology: Active Backup for Microsoft 365 | Official source |
| Backs up Exchange Online (mail, contacts, calendars), OneDrive for Business, SharePoint Online document libraries and lists, and Teams posts and settings. | Synology: technical specifications (DSM 7.3) | Official source |
| Scheduled, manual and continuous backup modes; retention either for a set period or all versions, with unlimited recovery points. | Synology: technical specifications (DSM 7.3) | Official source |
| Exports mail to EML or PST, contacts to CSV, calendars to ICS and Teams posts to HTML. | Synology: technical specifications (DSM 7.3) | Official source |
| Active Backup for Microsoft 365 version 3.0.0 moved the services that Microsoft Graph supports to Graph, and mail restores use Graph (permission MailboxItem.ImportExport.All). Backup and restore of archive mail, group mail and group calendars, and services hosted in the China region, still use the EWS API, so an admin has to keep EWS enabled and add the app ID to the EWSAllowedAppIDs list. Synology plans to move the remaining services if Graph adds the support, may discontinue them if it does not, and names 1 April 2027 as the date Microsoft discontinues EWS. | Synology Knowledge Center: EWS API error, permission error or 403 Forbidden during Microsoft 365 backups or restores | Official source |
| No automated restore verification was described on the pages checked, and no IMAP backup. | Synology: technical specifications (DSM 7.3) | Checked: not found |
Frequently asked
Is Synology Active Backup for Microsoft 365 really free?
Yes. Synology calls it a free add-on for Synology NAS servers and states that no licenses are required. The cost is the NAS and its disks.
Is Restow free too?
Restow Community is free for one organization, with no mailbox limit. Business and Service Provider are one-time purchases for features such as the audit log viewer, team roles, scheduled reports and, with Service Provider, multiple tenants. Pre-sale licenses include every 1.x update; from version 1.0, a license includes 12 months of updates, then an optional update year (Business €295, Service Provider €595 net per year).
Does Restow back up SharePoint and Teams like Synology?
In part. Restow has backed up SharePoint Online sites since 0.4.0 (document libraries and lists); the feature is new and so far tested against a simulated Microsoft Graph. Teams posts are not backed up; Synology covers them and Restow does not.