Microsoft 365 Backup: Veeam vs. CubeBackup vs. Open Source

There’s a clause in Microsoft’s terms of service that surprisingly few people have read: You are responsible for your own data in Microsoft 365. Microsoft guarantees the availability of the service—not the recoverability of your content.

No one notices this misunderstanding as long as nothing goes wrong. It becomes apparent when an employee is deleted after leaving the company, three months pass, and then someone needs the project files from that employee’s OneDrive.

What Needs to Be Backed Up

Four workloads, and all four matter:

Teams is the most problematic scenario because the data is scattered across different locations: files in SharePoint, chats in Exchange mailboxes, and structure in Azure AD. If you only back up mailboxes, you haven’t backed up Teams.

The Three Approaches

Veeam Backup for Microsoft 365

The market leader, and for good reason. All four workloads, highly granular recovery down to individual emails and file versions, freely selectable storage destination—local, S3-compatible, Azure. Licensed per user per year.

Pros: Maturity, market penetration, comprehensive support, seamless integration into existing Veeam environments. If you’re already using Veeam for virtual machines, you get a single console for both.

Cons: The price per user adds up, and you need a Windows machine for the proxy. For an operation with 100 mailboxes, this represents a significant annual expense.

CubeBackup

Significantly leaner, significantly cheaper, and often a better fit for a medium-sized business. It also backs up all four workloads and stores the data in an open format on the storage of your choice—local disk, NAS, or S3-compatible object storage.

Pros: A one-time license instead of a subscription, full control over data storage, low resource requirements.

Cons: Smaller provider, smaller community, fewer integrations. The recovery interface is functional but not as polished as Veeam’s.

We use CubeBackup: all four workloads, two years of retention, a 24-hour recovery target. For a company of our size, this is the right solution.

Open Source

Here’s where things get uncomfortably honest. In the summer of 2026, we had concrete plans to switch to an open-source solution—and then scrapped them.

The candidate looked good on paper: active development, modern architecture, a suitable feature set. Then we did what you should do with any OSS adoption—we didn’t read the project page, but instead checked the issue tracker:

• The repository was five months old.
• It had two stars.
• Of the open bugs, 34 had been reported by the developer himself.
• Three of them described silent bugs—backup runs that were reported as successful without actually being complete.

A backup that is silently incomplete is worse than none at all, because it gives a false sense of security. The migration was canceled.

That doesn’t mean open source fundamentally fails in this area. There are usable tools for Exchange alone. But as of mid-2026, there is no mature, open-source solution that reliably backs up all four M365 workloads—and anyone who claims otherwise hasn’t read the issue tracker.

The Comparison in a Table

What We Recommend

For a typical operation with 50 to 250 mailboxes, CubeBackup offers the best balance of cost, control, and maturity. For several hundred users or more—or if Veeam is already in use—Veeam has the edge due to its integration with existing operations.

And three things that apply regardless of the tool:

1. An archive is no substitute for a backup. MailStore and similar solutions address a compliance issue, not a recovery issue.
2. Store backups outside of Microsoft. A backup within the same tenant protects against deletion, not against a compromised tenant.
3. Test recovery, not the backup. A green checkmark proves nothing. Perform a real, logged restore twice a year—that’s the only proof that counts.

Further Reading

• Email Archiving and GoBD
• 3-2-1 Backup with Proxmox
• Self-Hosted NIS2