Hello @Shweta Mathur ,
Here is my code Java :

private static final String AUTHORITY = "https://login.microsoftonline.com/%s/oauth2/v2.0/token";
    private static final String GRANT_TYPE = "client_credentials";
    private static final String RESOURCE = "https://outlook.office365.com/.default";
    final static String clientId = "myClientId";
     final static String clientSecret = "myClientSecret";
     final static String tenantId = "myTenantId";
    private final String username;
    private final String accessToken;
    public EmailClient(String username, String accessToken) {
        this.username = username;
        this.accessToken = accessToken;
    public void connect() throws Exception {
        String host = "outlook.office365.com";
        String protocol = "imaps";
        int port = 993;
        Properties properties = new Properties();
        properties.put("mail.imaps.host", host);
        properties.put("mail.imaps.port", port);
        properties.put("mail.imaps.starttls.enable", "true");
        properties.put("mail.imaps.auth.login.disable", "true");
        properties.put("mail.imaps.auth.plain.disable", "true");
        properties.put("mail.imaps.sasl.enable", "true");
        properties.put("mail.imaps.sasl.mechanisms", "XOAUTH2");
        properties.put("mail.imap.sasl.oauth2.scope", RESOURCE);
        properties.put("mail.imaps.sasl.authorizationid", username);
        properties.put("mail.imaps.sasl.oauth2.access.token", accessToken);
        Session session = Session.getInstance(properties);
        IMAPStore store = (IMAPStore) session.getStore(protocol);
        store.connect(host, port, username, accessToken);
        Folder inbox = store.getFolder("inbox");
        inbox.open(Folder.READ_ONLY);
      Message[] messages = inbox.getMessages();
      for (Message message : messages) {
        File file = new File("email-" + message.getSubject() + ".eml");
        try (FileOutputStream fos = new FileOutputStream(file)) {
          message.writeTo(fos);
      inbox.close();
      store.close();
    public static String getAccessToken() throws IOException {
        String authority = String.format(AUTHORITY, tenantId);
        String encodedCredentials = Base64.getEncoder().encodeToString((clientId + ":" + clientSecret).getBytes());
        URL url = new URL(authority);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Authorization", "Basic " + encodedCredentials);
        conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
        Map<String, String> params = new HashMap<>();
        params.put("grant_type", GRANT_TYPE);
        params.put("scope", RESOURCE);
        String postData = getPostData(params);
        conn.setDoOutput(true);
        conn.getOutputStream().write(postData.getBytes());
        String response = "";
        Scanner scanner = new Scanner(conn.getInputStream());
        while (scanner.hasNext()) {
            response += scanner.nextLine();
        scanner.close();
        String accessToken = response.substring(response.indexOf("\"access_token\":\"") + 16);
        accessToken = accessToken.substring(0, accessToken.indexOf("\""));
        System.out.println(accessToken);
        return accessToken;
    private static String getPostData(Map<String, String> params) throws IOException {
        StringBuilder postData = new StringBuilder();
        for (Map.Entry<String, String> param : params.entrySet()) {
            if (postData.length() != 0) {
                postData.append('&');
            postData.append(URLEncoder.encode(param.getKey(), "UTF-8"));
            postData.append('=');
            postData.append(URLEncoder.encode(String.valueOf(param.getValue()), "UTF-8"));
        return postData.toString();
I am facing issue while try to access the microsoft mailbox using the access token and oAuth2.
With this implementation i get my acces token with all permission that i have added with my application Azure Microsoft.  

I am using the javamail to connect, but getting the below error.
Exception in thread "main" javax.mail.AuthenticationFailedException: AUTHENTICATE failed.
	at com.sun.mail.imap.IMAPStore.protocolConnect(IMAPStore.java:732)
	at javax.mail.Service.connect(Service.java:366)
	at routines.Email.main(Email.java:54)
												
Hi @javax.mail.AuthenticationFailedException  ,
Thanks for reaching out.
Could you please confirm which protocol and OAuth flow you are using to get the access token? 
So would elaborate on the steps taken to access the mailbox.
Thanks,
Shweta
						
Hi @javax.mail.AuthenticationFailedException   ,
Thanks for updating the question in detail.
As per the above code, you are using IMAP OAuth protocol with client credential flow to get the access token.
You are not able to authenticate successfully as the service principal has not been registered successfully.
For client credentials flow, you need to add application permissions under Office 365 Exchange Online
Make sure to grant admin consent for all the application permissions.
Once consent has been provided, the admin must register your AAD application's service principal in Exchange using powerShell by following commands:
Install ExchangeOnlineManagement
Install-Module -Name ExchangeOnlineManagement -allowprerelease Import-module ExchangeOnlineManagement Connect-ExchangeOnline -Organization
Register Service Principal in Exchange:
1.New-ServicePrincipal -AppId <APPLICATION_ID> -ServiceId <OBJECT_ID> [-Organization <ORGANIZATION_ID>]
Make sure to use ObjectId from enterprise applications rather than object id of application registration.  

For the same application you registered in Application Registration. A corresponding application has been created in Enterprise Application as well. You need to pass object id from there while registering service principal in Exchange:
2.Get-ServicePrincipal | fl
3.Add-MailboxPermission -Identity "john.smith@contoso.com" -User <SERVICE_PRINCIPAL_ID> -AccessRights FullAccess
In the application, you need to use scope = 'https://outlook.office365.com/.default '
Once you get the access token, you can create and open a Java Mail connection to read mails.
Properties props = new Properties();
props.put("mail.store.protocol", "imap");
props.put("mail.imap.host", "outlook.office365.com");
props.put("mail.imap.port", "993");
props.put("mail.imap.ssl.enable", "true");
props.put("mail.imap.starttls.enable", "true");
props.put("mail.imap.auth", "true");
props.put("mail.imap.auth.mechanisms", "XOAUTH2");
props.put("mail.imap.user", mailAddress);
props.put("mail.debug", "true");
props.put("mail.debug.auth", "true");
// open mailbox....
String token = getAuthToken(tanantId,clientId,client_secret);
Session session = Session.getInstance(props);
session.setDebug(true);
Store store = session.getStore("imap");
store.connect("outlook.office365.com", mailAddress, token);
Hope this will help.
Thanks,
Shweta
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