Java: Get mail as an app

Question

While using the msgraph-sdk-java to access mailbox by application only .
I can list all users.
When I try to list all mail by the below method ,


public static MessageCollectionResponse listMail(String userId) throws Exception {
    // /users/{id | userPrincipalName}/messages/{id}/attachments/{id}/$value
    if (_appClient == null) {
        throw new Exception("Graph has not been initialized for app-only auth");
    }
    //GET /users/{id | userPrincipalName}/messages
    return _appClient.users().byUserId(userId).messages().get(requestConfiguration -> {
        requestConfiguration.queryParameters.select = new String []{"sender", "subject"};
    });
}


 it response 401 .

Does this need to access with a user?


<dependency>
    <groupId>com.microsoft.graph</groupId>
    <artifactId>microsoft-graph</artifactId>
    <version>6.33.0</version>
</dependency>

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-identity</artifactId>
    <version>1.11.0</version>
</dependency>

Answer 1

Hi @WuWanning

Please check the following:

• Make sure the calling app has been assigned one of the Mail.ReadBasic.All, Mail.ReadWrite and Mail.Read application permissions and has been consented by the administrator.
• Make sure you are requesting the access token in the context of the application only (client credentials flow).
• Make sure the target user has a valid Microsoft 365 license and is not a guest user.
• Make sure your administrator has not restricted the application permissions to specific Exchange Online mailboxes.

Hope this helps.

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