MailStore Server alternative and comparison 2026
MailStore Server, owned by OpenText, is a self-hosted email archive for Windows. It is licensed per user with a perpetual right of use and a separate Update & Support subscription, and it holds an IDW PS 880 certification in Germany, Austria and Switzerland.
By Lucas Flores, IT Systeme Flores UG. Last updated
MailStore documentation checked on 2026-09-23 and 2026-09-24.
The short answer
MailStore fits companies that need a certified email archive on Windows today, with a perpetual license and a large installed base in German-speaking countries.
Restow fits if you want backup, restore and an archive in one Linux installation, with a weekly restore test. Its archive has a hash chain and search in every edition, plus capture from the mailboxes, journaling, retention and legal hold from Business, but no third-party certification; MailStore has the longer track record.
At a glance
| Aspect | Restow | MailStore |
|---|---|---|
| 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. | Per user, perpetual right of use, plus Update & Support for 1 to 3 years. Reactivating lapsed support costs 70 % of the current list price. |
| Where it runs | Self-hosted: one Docker Compose stack on a Linux server or VM you control. | Self-hosted on Windows; Windows Server above 25 users. |
| 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. | File system or NAS. No S3, Object Lock or WORM documented. |
| 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. | Email archiving for Microsoft 365, Exchange, Google and IMAP. |
| 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. | A schedulable integrity check (VerifyStore); no automated test-restore documented. |
| 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 openly specified. Exports as EML, MSG or PST. |
Where MailStore is strong
- IDW PS 880 certification for Germany, Austria and Switzerland.
- A perpetual license: the software keeps running after support lapses.
- Mature, widely used archive with many export paths.
- Signed exports can be verified with OpenSSL.
Where Restow is different
- Linux and Docker instead of Windows Server.
- S3-compatible object storage as well as local disk or NFS.
- Backup and non-destructive restore of whole mailboxes and OneDrive, with a weekly restore test.
- 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). The update year is priced per edition, not per user, and after a gap the next one costs the normal price, with no back payment.
Where do the GoBD come in?
Both products are used for email archiving in Germany, where the GoBD apply. Restow's archive is designed for GoBD-compliant use and is not certified; what the GoBD require for email, what Restow covers and what stays your job is set out on email archiving under the GoBD.
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.
MailStore: the facts, with sources
Each line is taken from MailStore'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 |
|---|---|---|
| Self-hosted, Windows only. Once an installation passes 25 users, a full Windows Server edition is required. | System Requirements | Official source |
| Licensed per user with a perpetual right of use. A separate, time-limited Update & Support subscription (1, 2 or 3 years, Standard or Premium) is sold alongside it; the software keeps running after that subscription lapses. | Ordering and Licensing FAQ | Official source |
| Reactivating a lapsed Update & Support subscription is not a normal renewal: the vendor's own published terms price it as an "upgrade" at 70% of the current list price of the existing licenses. | Ordering and Licensing FAQ | Official source |
| A starter package covers 5 users. | Ordering and Licensing FAQ | Official source |
| An IDW PS 880 software certification exists for Germany, Austria and Switzerland: a real, named German auditing-standard certificate, not a self-declared claim. Publicly downloadable certificate PDFs go up to version 23.4; the current certificate is available on request. | Rechtssicherheit (legal certainty) | Official source |
| Storage is file system or NAS. SQL/PostgreSQL-backed stores have taken no new installations since version 26.1 and are being phased out entirely by the end of 2026. No S3, Object Lock or WORM storage support is documented. | Storage Locations | Official source |
| Export formats: EML/MSG, PST, or direct export into an M365/Exchange/Google/IMAP mailbox with folder structure preserved; signed exports can be verified with OpenSSL. The internal storage format itself is not openly specified. | Exporting Email | Official source |
| A schedulable integrity check ("VerifyStore") exists; an automated end-to-end test-restore comparable to reading data back and diffing it is not documented. | Maintenance and Repair | Official source |
| Not open source: proprietary commercial software owned by OpenText. | Absence checked across the pages above | Checked: not found |
Frequently asked
Does Restow also archive email, like MailStore?
Yes, with limits, since 0.1.0: every edition has an archive with a SHA-256 hash chain, chain verification, export and search over subject, addresses and the body text of imported mail (not attachments), filled by mail import with archiving. Business and Service Provider add capture from the mailboxes, since 0.4.4: Microsoft 365 by Microsoft Graph and IMAP and Google Workspace by IMAP sync, both near-time and not complete, plus Exchange Online journal receipt and copies a mail provider forwards, which capture in transport, enforced retention and legal hold. The new ways were tested against simulated services only. MailStore holds an IDW PS 880 certificate; Restow has none, and is younger.
What happens when MailStore Update & Support lapses?
The software keeps running. Reactivating support later is priced as an upgrade at 70 % of the current list price of your licenses, according to MailStore's published terms.
Can I move from MailStore to Restow?
Partly. Restow imports a MailStore export as EML or MSG files (a folder tree, or a ZIP of it) into a legacy mailbox that you can browse, restore into Microsoft 365 or IMAP, download and optionally archive. MailStore's internal archive format cannot be read, so export from MailStore first. Restow exports mail as EML in a ZIP or as MBOX, with checksums; PST export is planned.