Backup Fails Due to Microsoft Graph API Restrictions

Product version: 11.0

Last modified: 25 July 2025

Problem

When backing up or accessing Microsoft 365 mailboxes via NAKIVO Backup & Replication, you may encounter the following error message:

REST API is not yet supported.

REST API is not yet supported for mailbox "<MailboxName>".

This error occurs when Microsoft Graph cannot access the target mailbox, typically due to licensing, provisioning, or unsupported mailbox types.

Background

NAKIVO Backup & Replication uses the Microsoft Graph API to discover and access Microsoft 365 user data, including mailbox content. However, not all mailbox types are supported by the Graph API. This issue may occur due to one or more of the following reasons:

  • The user has never signed in to their mailbox (mailbox not fully provisioned).

  • The user does not have an Exchange Online license assigned.

  • The mailbox is a shared or resource mailbox with limited or no support for Microsoft Graph REST API operations.

  • The mailbox is hosted on-premises in a hybrid environment and is not accessible via Microsoft Graph.

  • The mailbox is still being provisioned (e.g., shortly after license assignment).

  • The mailbox is disabled or inactive.

  • The mailbox was recently converted (e.g., from user to shared) and has not yet been fully updated across services.

  • The mailbox is a public folder mailbox, which is not supported by Microsoft Graph.

  • The mailbox is a legacy mailbox type that is incompatible with REST APIs.

  • The mailbox is hosted on-premises and not synced or migrated to Exchange Online.

  • The mailbox is a resource mailbox with limited support in the Graph API.

  • The mailbox is in a disconnected or soft-deleted state.

  • The mailbox is associated with a service account or another non-user entity.

Solution

To resolve this issue, follow the steps below:

  1. Ensure the user has a valid Microsoft 365 license. Assign a license that includes Exchange Online (e.g., E3, E5, or Business Standard).

  2. Ask the user to sign in to their mailbox at least once. REST API access (e.g., via Microsoft Graph) is not enabled until the mailbox is fully provisioned after the first login.

  3. Wait a few minutes after assigning the license. Provisioning may take some time. Retry after a short delay.

  4. Avoid using shared/resource mailboxes unless supported.

  5. REST APIs do not support all operations on non-user mailboxes.

  6. Verify mailbox status. Make sure the mailbox is active and not disabled or in a soft-deleted state.

  7. Ensure the mailbox is hosted in Exchange Online. REST APIs such as Microsoft Graph cannot access on-premises mailboxes.

  8. Verify the mailbox type. Ensure it is a user mailbox and not a public folder, resource, or legacy type.

  9. Migrate the mailbox to Exchange Online. REST APIs only support Exchange Online mailboxes.

  10. Avoid using unsupported mailbox types. Public folders, disconnected mailboxes, and some hybrid configurations are not supported.

  11. Review Microsoft Graph API documentation. Ensure your use case is compatible with Graph API limitations for mailbox access: