(click to expand table of contents)
4. Authentication and Security
4.1. Modern Authentication
When using this method, Veeam Backup for Microsoft Office 365 uses an Azure AD application for an authentication process against the Office 365 organizations with enabled security defaults; you cannot use a user account with the modern authentication method. Multi-factor authentication would be enabled.
4.2. Modern Authentication with Legacy Authentication Protocols
When using this method, you can use both the user account and the Azure AD application to authenticate against your Office 365 organizations with disabled security defaults.
Microsoft is planning to cease the use of legacy authentication.
4.3. Basic Authentication
When using this method, you are required to provide a user account and its password to authenticate against your Office 365 organization.
See the help section for more info: https://helpcenter.veeam.com/docs/vbo365/guide/vbo_add_office365_org.html?ver=40