Microsoft 365 Exchange Online backup

Microsoft 365 Backup covers Exchange Online mailboxes and online archives when they are included in a backup policy. The bill is driven by the total protected gigabytes, not by user count, so large archives and recoverable-items folders can turn a cheap mailbox plan into an expensive backup line item.

What is protected

• Primary Exchange Online mailboxes in the policy.
• Online archive mailboxes, if explicitly included.
• Recoverable items, including deleted-item retention and litigation hold content that is part of the mailbox.

What inflates the mailbox portion of the bill

The per-GB rate of $0.15 applies to the protected size of each mailbox. The size reported in the admin centre is usually only the primary mailbox. The admin centre does not show the online archive or the recoverable-items folder in the same view, so a sizing exercise based only on the visible number will understate the real backup cost.

This matters most for long-tenured staff and former employees. Mailboxes that were migrated from on-premises Exchange, or that have been on litigation hold, can be several times larger than the headline figure. The PowerShell mailbox-size script returns primary, archive and recoverable-items sizes in one export so you can price accurately.

Retention and restore limits

Backups are kept for up to one year. Point-in-time restores go back to protected recovery points within that window. There is no option to keep backups longer, and no way to export a mailbox backup outside Microsoft's cloud. If you need multi-year retention or an offline copy, a third party is required.

Shared mailboxes and resource mailboxes

Shared mailboxes and resource mailboxes are not automatically covered by user-level policies. If they hold data the business would need back, they must be explicitly added to the backup policy. Because they are often unlicensed and unmanaged, these mailboxes are a common gap.

When Exchange Online backup is enough

For organisations whose main risk is accidental deletion or limited ransomware recovery, and whose mailbox data fits comfortably under one year of retention, native backup is usually the simplest and cheapest option. The cost grows with archive size, so the moment long-term archives or litigation holds become common, the per-GB bill deserves a careful look.

Calculate Exchange Online backup cost What native backup doesn't cover

Frequently asked questions