diff --git a/src/cli.py b/src/cli.py
index 54defe3..35cf3e0 100644
--- a/src/cli.py
+++ b/src/cli.py
@@ -12,6 +12,7 @@ from src.email_providers.base import MockProvider
 from src.email_providers.gmail import GmailProvider
 from src.email_providers.imap import IMAPProvider
 from src.email_providers.enron import EnronProvider
+from src.email_providers.outlook import OutlookProvider
 from src.classification.feature_extractor import FeatureExtractor
 from src.classification.ml_classifier import MLClassifier
 from src.classification.llm_classifier import LLMClassifier
@@ -27,7 +28,7 @@ def cli():
 
 
 @cli.command()
-@click.option('--source', type=click.Choice(['gmail', 'imap', 'mock', 'enron']), default='mock',
+@click.option('--source', type=click.Choice(['gmail', 'outlook', 'imap', 'mock', 'enron']), default='mock',
               help='Email provider')
 @click.option('--credentials', type=click.Path(exists=False),
               help='Path to credentials file')
@@ -85,6 +86,11 @@ def run(
         if not credentials:
             logger.error("Gmail provider requires --credentials")
             sys.exit(1)
+    elif source == 'outlook':
+        provider = OutlookProvider()
+        if not credentials:
+            logger.error("Outlook provider requires --credentials")
+            sys.exit(1)
     elif source == 'imap':
         provider = IMAPProvider()
         if not credentials:
diff --git a/src/email_providers/outlook.py b/src/email_providers/outlook.py
new file mode 100644
index 0000000..b671cf0
--- /dev/null
+++ b/src/email_providers/outlook.py
@@ -0,0 +1,358 @@
+"""Microsoft Outlook/Office365 provider implementation using Microsoft Graph API.
+
+This provider connects to Outlook.com, Office365, and Microsoft 365 accounts
+using the Microsoft Graph API with OAuth 2.0 authentication.
+
+Authentication Setup:
+1. Register app at https://portal.azure.com/#blade/Microsoft_AAD_RegisteredApps
+2. Add Mail.Read and Mail.ReadWrite permissions
+3. Get client_id and client_secret
+4. Configure redirect URI (http://localhost:8080 for development)
+"""
+import logging
+from typing import List, Dict, Optional, Any
+from datetime import datetime
+from email.utils import parsedate_to_datetime
+
+from .base import BaseProvider, Email, Attachment
+
+logger = logging.getLogger(__name__)
+
+
+class OutlookProvider(BaseProvider):
+    """
+    Microsoft Outlook/Office365 email provider via Microsoft Graph API.
+
+    Supports:
+    - Outlook.com personal accounts
+    - Office365 business accounts
+    - Microsoft 365 accounts
+
+    Authentication:
+    - OAuth 2.0 with Microsoft Identity Platform
+    - Requires app registration in Azure Portal
+    - Uses delegated permissions (Mail.Read, Mail.ReadWrite)
+    """
+
+    def __init__(self):
+        """Initialize Outlook provider."""
+        super().__init__(name="outlook")
+        self.client = None
+        self.user_id = None
+        self._credentials_configured = False
+
+    def connect(self, credentials: Dict[str, Any]) -> bool:
+        """
+        Connect to Microsoft Graph API using OAuth credentials.
+
+        Args:
+            credentials: Dict containing:
+                - client_id: Azure AD application ID
+                - client_secret: Azure AD application secret (optional for desktop apps)
+                - tenant_id: Azure AD tenant ID (optional, defaults to 'common')
+                - redirect_uri: OAuth redirect URI (default: http://localhost:8080)
+
+        Returns:
+            True if connection successful, False otherwise
+        """
+        try:
+            client_id = credentials.get('client_id')
+            if not client_id:
+                logger.error(
+                    "OUTLOOK OAUTH NOT CONFIGURED: "
+                    "client_id required in credentials. "
+                    "Register app at: "
+                    "https://portal.azure.com/#blade/Microsoft_AAD_RegisteredApps"
+                )
+                return False
+
+            # TRY IMPORT - will fail if msal not installed
+            try:
+                import msal
+                import requests
+            except ImportError as e:
+                logger.error(f"OUTLOOK DEPENDENCIES MISSING: {e}")
+                logger.error("Install with: pip install msal requests")
+                return False
+
+            # TRY CONNECTION - authenticate with Microsoft
+            tenant_id = credentials.get('tenant_id', 'common')
+            client_secret = credentials.get('client_secret')
+            redirect_uri = credentials.get('redirect_uri', 'http://localhost:8080')
+
+            authority = f"https://login.microsoftonline.com/{tenant_id}"
+            scopes = ["https://graph.microsoft.com/Mail.Read",
+                     "https://graph.microsoft.com/Mail.ReadWrite"]
+
+            logger.info(f"Attempting Outlook OAuth with client_id: {client_id[:8]}...")
+
+            # Create MSAL app (public client for desktop, confidential for server)
+            if client_secret:
+                app = msal.ConfidentialClientApplication(
+                    client_id,
+                    authority=authority,
+                    client_credential=client_secret
+                )
+            else:
+                app = msal.PublicClientApplication(
+                    client_id,
+                    authority=authority
+                )
+
+            # Try to get token - interactive flow for desktop apps
+            result = None
+
+            # First try cached token
+            accounts = app.get_accounts()
+            if accounts:
+                result = app.acquire_token_silent(scopes, account=accounts[0])
+
+            # If no cached token, do interactive login
+            if not result:
+                flow = app.initiate_device_flow(scopes=scopes)
+                if "user_code" not in flow:
+                    logger.error("Failed to create device flow")
+                    return False
+
+                logger.info("\n" + "="*60)
+                logger.info("MICROSOFT AUTHENTICATION REQUIRED")
+                logger.info("="*60)
+                logger.info(flow["message"])
+                logger.info("="*60 + "\n")
+
+                result = app.acquire_token_by_device_flow(flow)
+
+            if "access_token" not in result:
+                logger.error(f"OUTLOOK AUTHENTICATION FAILED: {result.get('error_description', 'Unknown error')}")
+                return False
+
+            # Store access token and create Graph API client
+            self.access_token = result['access_token']
+            self.graph_client = requests.Session()
+            self.graph_client.headers.update({
+                'Authorization': f'Bearer {self.access_token}',
+                'Content-Type': 'application/json'
+            })
+
+            # Get user profile to verify connection
+            response = self.graph_client.get('https://graph.microsoft.com/v1.0/me')
+            if response.status_code == 200:
+                user_info = response.json()
+                self.user_id = user_info.get('id')
+                logger.info(f"Successfully connected to Outlook for: {user_info.get('userPrincipalName')}")
+                self._credentials_configured = True
+                return True
+            else:
+                logger.error(f"Failed to verify Outlook connection: {response.status_code}")
+                return False
+
+        except Exception as e:
+            logger.error(f"OUTLOOK CONNECTION FAILED: {e}")
+            import traceback
+            logger.debug(traceback.format_exc())
+            return False
+
+    def disconnect(self) -> bool:
+        """Close Outlook connection."""
+        self.graph_client = None
+        self.access_token = None
+        self.user_id = None
+        self._credentials_configured = False
+        logger.info("Disconnected from Outlook")
+        return True
+
+    def fetch_emails(
+        self,
+        limit: Optional[int] = None,
+        filters: Optional[Dict[str, Any]] = None
+    ) -> List[Email]:
+        """
+        Fetch emails from Outlook via Microsoft Graph API.
+
+        Args:
+            limit: Maximum number of emails to fetch
+            filters: Optional filters (folder, search query, etc.)
+
+        Returns:
+            List of Email objects
+        """
+        if not self._credentials_configured or not self.graph_client:
+            logger.error("OUTLOOK NOT CONFIGURED: Cannot fetch emails without OAuth setup")
+            return []
+
+        emails = []
+        try:
+            # Build Graph API query
+            folder = filters.get('folder', 'inbox') if filters else 'inbox'
+            search_query = filters.get('query', '') if filters else ''
+
+            # Construct Graph API URL
+            url = f"https://graph.microsoft.com/v1.0/me/mailFolders/{folder}/messages"
+            params = {
+                '$top': min(limit or 500, 1000) if limit else 500,
+                '$orderby': 'receivedDateTime DESC'
+            }
+
+            if search_query:
+                params['$search'] = f'"{search_query}"'
+
+            # Fetch messages
+            response = self.graph_client.get(url, params=params)
+
+            if response.status_code != 200:
+                logger.error(f"Failed to fetch emails: {response.status_code} - {response.text}")
+                return []
+
+            data = response.json()
+            messages = data.get('value', [])
+
+            for msg in messages:
+                email = self._parse_message(msg)
+                if email:
+                    emails.append(email)
+                    if limit and len(emails) >= limit:
+                        break
+
+            logger.info(f"Fetched {len(emails)} emails from Outlook")
+            return emails
+
+        except Exception as e:
+            logger.error(f"OUTLOOK FETCH ERROR: {e}")
+            import traceback
+            logger.debug(traceback.format_exc())
+            return emails
+
+    def _parse_message(self, msg: Dict) -> Email:
+        """Parse Microsoft Graph message into Email object."""
+        try:
+            # Parse sender
+            sender_email = msg.get('from', {}).get('emailAddress', {}).get('address', '')
+
+            # Parse date
+            date_str = msg.get('receivedDateTime')
+            date = datetime.fromisoformat(date_str.replace('Z', '+00:00')) if date_str else None
+
+            # Parse body
+            body_content = msg.get('body', {})
+            body = body_content.get('content', '')
+
+            # Parse attachments
+            has_attachments = msg.get('hasAttachments', False)
+            attachments = []
+            if has_attachments:
+                attachments = self._parse_attachments(msg.get('id'))
+
+            return Email(
+                id=msg.get('id'),
+                subject=msg.get('subject', 'No Subject'),
+                sender=sender_email,
+                date=date,
+                body=body,
+                has_attachments=has_attachments,
+                attachments=attachments,
+                headers={'message-id': msg.get('id')},
+                labels=msg.get('categories', []),
+                is_read=msg.get('isRead', False),
+                provider='outlook'
+            )
+
+        except Exception as e:
+            logger.error(f"Error parsing message: {e}")
+            return None
+
+    def _parse_attachments(self, message_id: str) -> List[Attachment]:
+        """Fetch and parse attachments for a message."""
+        attachments = []
+
+        try:
+            url = f"https://graph.microsoft.com/v1.0/me/messages/{message_id}/attachments"
+            response = self.graph_client.get(url)
+
+            if response.status_code == 200:
+                data = response.json()
+                for att in data.get('value', []):
+                    attachments.append(Attachment(
+                        filename=att.get('name', 'unknown'),
+                        mime_type=att.get('contentType', 'application/octet-stream'),
+                        size=att.get('size', 0),
+                        attachment_id=att.get('id')
+                    ))
+        except Exception as e:
+            logger.debug(f"Error fetching attachments: {e}")
+
+        return attachments
+
+    def update_labels(self, email_id: str, labels: List[str]) -> bool:
+        """Update categories for a single email."""
+        if not self._credentials_configured or not self.graph_client:
+            logger.error("OUTLOOK NOT CONFIGURED: Cannot update labels")
+            return False
+
+        try:
+            url = f"https://graph.microsoft.com/v1.0/me/messages/{email_id}"
+            data = {"categories": labels}
+
+            response = self.graph_client.patch(url, json=data)
+
+            if response.status_code in [200, 204]:
+                return True
+            else:
+                logger.error(f"Failed to update labels: {response.status_code}")
+                return False
+
+        except Exception as e:
+            logger.error(f"Error updating labels: {e}")
+            return False
+
+    def batch_update(self, updates: List[Dict[str, Any]]) -> bool:
+        """Batch update multiple emails."""
+        if not self._credentials_configured or not self.graph_client:
+            logger.error("OUTLOOK NOT CONFIGURED: Cannot batch update")
+            return False
+
+        try:
+            # Microsoft Graph API supports batch requests
+            batch_requests = []
+
+            for i, update in enumerate(updates):
+                email_id = update.get('email_id')
+                labels = update.get('labels', [])
+
+                batch_requests.append({
+                    "id": str(i),
+                    "method": "PATCH",
+                    "url": f"/me/messages/{email_id}",
+                    "body": {"categories": labels},
+                    "headers": {"Content-Type": "application/json"}
+                })
+
+            # Send batch request (max 20 per batch)
+            batch_size = 20
+            successful = 0
+
+            for i in range(0, len(batch_requests), batch_size):
+                batch = batch_requests[i:i+batch_size]
+
+                response = self.graph_client.post(
+                    'https://graph.microsoft.com/v1.0/$batch',
+                    json={"requests": batch}
+                )
+
+                if response.status_code == 200:
+                    result = response.json()
+                    for resp in result.get('responses', []):
+                        if resp.get('status') in [200, 204]:
+                            successful += 1
+
+            logger.info(f"Batch updated {successful}/{len(updates)} emails")
+            return successful > 0
+
+        except Exception as e:
+            logger.error(f"Batch update error: {e}")
+            import traceback
+            logger.debug(traceback.format_exc())
+            return False
+
+    def is_connected(self) -> bool:
+        """Check if connected."""
+        return self._credentials_configured and self.graph_client is not None