Considerations and limitations when using different authentication methods

Starting with Veeam Backup for Microsoft Office version 4c, support for two different modern authentication methods for working with Office 365 organizations was created. Depending on your Office 365 tenant configuration and the restrictions on using legacy authentication protocols, you can either use a modern app-only authentication for tenants with disabled legacy protocols or use a modern authentication through an MFA-enabled service account and a pre-configured Azure AD application.   
When protecting Office 365 organizations that use modern application-only authentication, consider the following limitations in backup and restore functionality:

Backup

• Discovery Search and Public Folder mailboxes are not supported.
• Dynamic Distribution groups are not supported.
• The type property for shared and resource/equipment mailboxes cannot be resolved. Such mailboxes will be available for backup with a general ‘User’ type (Note: This limitation only applies to creating a backup jobs and does not affect licensing).
• SharePoint Web Parts can only be backed up if their ‘exportmode’ property is enabled. Non-exportable Web Parts are not supported. 

Restore

• OneNote restore is not supported.
• SharePoint Web Part customized template cannot be preserved upon a restore. All Web Parts will be restored with the default template.
• The ‘Allow multiple responses’ setting in survey lists within team modern sites is not preserved upon a restore.
  
  

PowerShell

• The ‘Measure-VBOOrganizationFullBackupSize’ cmdlet is not supported.