diff --git a/lib/services/caldav-sync.ts b/lib/services/caldav-sync.ts
index 01ad4db..cc1c86e 100644
--- a/lib/services/caldav-sync.ts
+++ b/lib/services/caldav-sync.ts
@@ -27,7 +27,8 @@ export async function getInfomaniakCalDAVClient(
   password: string
 ): Promise<WebDAVClient> {
   // Infomaniak CalDAV base URL (from Infomaniak sync assistant)
-  const baseUrl = 'https://sync.infomaniak.com';
+  // The actual CalDAV endpoint is at /caldav path
+  const baseUrl = 'https://sync.infomaniak.com/caldav';
   
   const client = createClient(baseUrl, {
     username: email,
diff --git a/lib/services/email-service.ts b/lib/services/email-service.ts
index f2c2108..f15b384 100644
--- a/lib/services/email-service.ts
+++ b/lib/services/email-service.ts
@@ -21,6 +21,12 @@ import { EmailCredentials, EmailMessage, EmailAddress, EmailAttachment } from '@
 import { ensureFreshToken } from './token-refresh';
 import { createXOAuth2Token, refreshAccessToken as refreshMicrosoftAccessToken } from './microsoft-oauth';
 import { MailCredentials } from '@prisma/client';
+import {
+  fetchGraphEmails as fetchGraphEmailsAPI,
+  fetchGraphMailFolders,
+  sendGraphEmail as sendGraphEmailAPI,
+  GraphMailMessage,
+} from './microsoft-graph-mail';
 import Redis from 'ioredis';
 import { getRedisClient } from '../redis';
 import { logger } from '@/lib/logger';
@@ -779,8 +785,123 @@ interface FetchOptions {
   bodyParts: { part: string; query: any; limit?: number }[];
 }
 
+/**
+ * Check if an account should use Microsoft Graph API instead of IMAP
+ */
+async function shouldUseGraphAPI(userId: string, accountId?: string): Promise<{ useGraph: boolean; mailCredentialId?: string }> {
+  try {
+    // Resolve accountId if it's 'default'
+    let resolvedAccountId = accountId;
+    if (!resolvedAccountId || resolvedAccountId === 'default') {
+      const accounts = await prisma.mailCredentials.findMany({
+        where: { userId },
+        orderBy: { createdAt: 'asc' },
+        take: 1
+      });
+      if (accounts && accounts.length > 0) {
+        resolvedAccountId = accounts[0].id;
+      }
+    }
+    
+    if (!resolvedAccountId) {
+      return { useGraph: false };
+    }
+    
+    // Check if this is a Microsoft account with OAuth
+    const mailCredential = await prisma.mailCredentials.findUnique({
+      where: { id: resolvedAccountId },
+      select: {
+        id: true,
+        host: true,
+        use_oauth: true,
+        refresh_token: true,
+      },
+    });
+    
+    if (mailCredential && 
+        mailCredential.host === 'outlook.office365.com' && 
+        mailCredential.use_oauth && 
+        mailCredential.refresh_token) {
+      return { useGraph: true, mailCredentialId: mailCredential.id };
+    }
+    
+    return { useGraph: false };
+  } catch (error) {
+    logger.error('[EMAIL] Error checking if should use Graph API', {
+      userId,
+      accountId,
+      error: error instanceof Error ? error.message : String(error),
+    });
+    return { useGraph: false };
+  }
+}
+
+/**
+ * Convert Graph API folder name to Graph API folder ID
+ * Graph API uses folder IDs, but we can map common names
+ */
+function mapFolderNameToGraphId(folderName: string): string {
+  const folderMap: Record<string, string> = {
+    'INBOX': 'Inbox',
+    'Sent': 'SentItems',
+    'Drafts': 'Drafts',
+    'Trash': 'DeletedItems',
+    'Junk': 'JunkEmail',
+    'Archive': 'Archive',
+  };
+  
+  return folderMap[folderName] || folderName;
+}
+
+/**
+ * Convert Graph API mail message to EmailMessage format
+ */
+function convertGraphMessageToEmailMessage(
+  graphMessage: GraphMailMessage,
+  folder: string,
+  accountId: string
+): EmailMessage {
+  return {
+    id: graphMessage.id,
+    from: graphMessage.from ? [{
+      name: graphMessage.from.emailAddress.name || '',
+      address: graphMessage.from.emailAddress.address,
+    }] : [],
+    to: graphMessage.toRecipients?.map(recipient => ({
+      name: recipient.emailAddress.name || '',
+      address: recipient.emailAddress.address,
+    })) || [],
+    cc: graphMessage.ccRecipients?.map(recipient => ({
+      name: recipient.emailAddress.name || '',
+      address: recipient.emailAddress.address,
+    })),
+    subject: graphMessage.subject || '',
+    date: new Date(graphMessage.receivedDateTime),
+    flags: {
+      seen: graphMessage.isRead,
+      flagged: graphMessage.flag?.flagStatus === 'flagged' || graphMessage.flag?.flagStatus === 'complete',
+      answered: false, // Graph API doesn't have this flag directly
+      draft: false, // Would need to check message type
+      deleted: false,
+    },
+    size: 0, // Graph API doesn't provide size directly in this format
+    hasAttachments: graphMessage.hasAttachments || false,
+    folder,
+    contentFetched: false,
+    accountId,
+    content: {
+      text: graphMessage.body?.contentType === 'text' ? (graphMessage.body.content || '') : '',
+      html: graphMessage.body?.contentType === 'html' ? (graphMessage.body.content || '') : (graphMessage.bodyPreview || ''),
+      isHtml: graphMessage.body?.contentType === 'html',
+      direction: 'ltr',
+    },
+    preview: graphMessage.bodyPreview,
+  };
+}
+
 /**
  * Get list of emails for a user
+ * Uses Graph API for Microsoft accounts, IMAP for others
  */
 export async function getEmails(
   userId: string,
@@ -801,6 +922,79 @@ export async function getEmails(
   });
   
   try {
+    // Check if we should use Graph API for Microsoft accounts
+    const graphCheck = await shouldUseGraphAPI(userId, accountId);
+    
+    if (graphCheck.useGraph && graphCheck.mailCredentialId) {
+      // Use Microsoft Graph API
+      logger.debug('[EMAIL] Using Microsoft Graph API', {
+        userId,
+        folder,
+        mailCredentialId: graphCheck.mailCredentialId,
+      });
+      
+      try {
+        const graphFolderId = mapFolderNameToGraphId(folder);
+        const skip = (page - 1) * perPage;
+        
+        // Fetch emails from Graph API
+        const graphResult = await fetchGraphEmailsAPI(
+          graphCheck.mailCredentialId,
+          graphFolderId,
+          perPage,
+          skip
+        );
+        
+        // Get mailboxes (folders)
+        const graphFolders = await fetchGraphMailFolders(graphCheck.mailCredentialId);
+        const mailboxes = graphFolders.map(f => f.displayName);
+        
+        // Convert Graph messages to EmailMessage format
+        const emails = graphResult.value.map(msg => 
+          convertGraphMessageToEmailMessage(msg, folder, accountId || 'default')
+        );
+        
+        // Calculate total (Graph API doesn't provide total count directly, so we estimate)
+        const totalEmails = graphResult['@odata.nextLink'] 
+          ? (page * perPage) + 1 // Has more pages
+          : emails.length;
+        
+        const result: EmailListResult = {
+          emails,
+          totalEmails,
+          page,
+          perPage,
+          totalPages: Math.ceil(totalEmails / perPage),
+          folder,
+          mailboxes,
+          newestEmailId: emails.length > 0 ? parseInt(emails[0].id) || 0 : 0,
+        };
+        
+        // Cache the result
+        if (!checkOnly) {
+          await cacheEmailList(
+            userId,
+            accountId || 'default',
+            folder,
+            page,
+            perPage,
+            result
+          );
+        }
+        
+        return result;
+      } catch (error) {
+        logger.error('[EMAIL] Error fetching emails from Graph API', {
+          userId,
+          folder,
+          error: error instanceof Error ? error.message : String(error),
+        });
+        // Fall back to IMAP if Graph API fails
+        logger.debug('[EMAIL] Falling back to IMAP after Graph API error');
+      }
+    }
+    
+    // Use IMAP for non-Microsoft accounts or as fallback
     // The getImapConnection function already handles 'default' accountId by finding the first available account
     const client = await getImapConnection(userId, accountId);
     
@@ -1387,9 +1581,52 @@ export async function sendEmail(
       content: string;
       type: string;
     }>;
-  }
+  },
+  accountId?: string
 ): Promise<{ success: boolean; messageId?: string; error?: string }> {
-  const credentials = await getUserEmailCredentials(userId);
+  // Check if we should use Graph API for Microsoft accounts
+  const graphCheck = await shouldUseGraphAPI(userId, accountId);
+  
+  if (graphCheck.useGraph && graphCheck.mailCredentialId) {
+    // Use Microsoft Graph API to send email
+    logger.debug('[EMAIL] Sending email via Microsoft Graph API', {
+      userId,
+      mailCredentialId: graphCheck.mailCredentialId,
+    });
+    
+    try {
+      const result = await sendGraphEmailAPI(graphCheck.mailCredentialId, {
+        to: emailData.to,
+        cc: emailData.cc,
+        bcc: emailData.bcc,
+        subject: emailData.subject,
+        body: emailData.body,
+        bodyType: 'html',
+        attachments: emailData.attachments?.map(att => ({
+          name: att.name,
+          content: att.content, // Should be base64 encoded
+          contentType: att.type,
+        })),
+      });
+      
+      return {
+        success: true,
+        messageId: result.id,
+      };
+    } catch (error) {
+      logger.error('[EMAIL] Error sending email via Graph API', {
+        userId,
+        error: error instanceof Error ? error.message : String(error),
+      });
+      return {
+        success: false,
+        error: error instanceof Error ? error.message : 'Unknown error',
+      };
+    }
+  }
+  
+  // Use SMTP for non-Microsoft accounts
+  const credentials = await getUserEmailCredentials(userId, accountId);
   
   if (!credentials) {
     return { 
diff --git a/lib/services/microsoft-graph-mail.ts b/lib/services/microsoft-graph-mail.ts
new file mode 100644
index 0000000..9987a94
--- /dev/null
+++ b/lib/services/microsoft-graph-mail.ts
@@ -0,0 +1,343 @@
+/**
+ * Microsoft Graph API Mail Service
+ * 
+ * This service replaces IMAP/SMTP for Microsoft accounts by using Graph API.
+ * It provides email reading, sending, and folder management capabilities.
+ */
+
+import axios, { AxiosInstance } from 'axios';
+import { ensureFreshToken } from './token-refresh';
+import { logger } from '@/lib/logger';
+import { prisma } from '@/lib/prisma';
+
+// Graph API base URL
+const GRAPH_API_BASE = 'https://graph.microsoft.com/v1.0';
+
+/**
+ * Get a configured Axios instance for Microsoft Graph API
+ */
+async function getMicrosoftGraphClient(mailCredentialId: string): Promise<AxiosInstance> {
+  // Get fresh access token
+  const tokenResult = await ensureFreshToken(mailCredentialId);
+  
+  if (!tokenResult || !tokenResult.accessToken) {
+    throw new Error('Failed to obtain valid access token for Microsoft Graph API. The account may need to be re-authenticated with Mail.Read and Mail.Send permissions.');
+  }
+
+  return axios.create({
+    baseURL: GRAPH_API_BASE,
+    headers: {
+      'Authorization': `Bearer ${tokenResult.accessToken}`,
+      'Content-Type': 'application/json',
+    },
+  });
+}
+
+/**
+ * Microsoft Graph Mail Message interface
+ */
+export interface GraphMailMessage {
+  id: string;
+  subject?: string;
+  from?: {
+    emailAddress: {
+      name?: string;
+      address: string;
+    };
+  };
+  toRecipients?: Array<{
+    emailAddress: {
+      name?: string;
+      address: string;
+    };
+  }>;
+  ccRecipients?: Array<{
+    emailAddress: {
+      name?: string;
+      address: string;
+    };
+  }>;
+  body?: {
+    contentType: 'text' | 'html';
+    content: string;
+  };
+  bodyPreview?: string;
+  receivedDateTime: string;
+  sentDateTime?: string;
+  isRead: boolean;
+  hasAttachments: boolean;
+  importance?: 'low' | 'normal' | 'high';
+  flag?: {
+    flagStatus: 'notFlagged' | 'flagged' | 'complete';
+  };
+}
+
+/**
+ * Microsoft Graph Mail Folder interface
+ */
+export interface GraphMailFolder {
+  id: string;
+  displayName: string;
+  parentFolderId?: string;
+  childFolderCount: number;
+  unreadItemCount: number;
+  totalItemCount: number;
+}
+
+/**
+ * Fetch emails from a Microsoft mailbox folder using Graph API
+ */
+export async function fetchGraphEmails(
+  mailCredentialId: string,
+  folderId: string = 'Inbox',
+  top: number = 50,
+  skip: number = 0,
+  filter?: string
+): Promise<{
+  value: GraphMailMessage[];
+  '@odata.nextLink'?: string;
+}> {
+  try {
+    const client = await getMicrosoftGraphClient(mailCredentialId);
+    
+    // Build the query URL
+    let url = `/me/mailFolders/${folderId}/messages`;
+    const params = new URLSearchParams({
+      '$top': top.toString(),
+      '$skip': skip.toString(),
+      '$orderby': 'receivedDateTime desc',
+      '$select': 'id,subject,from,toRecipients,ccRecipients,body,bodyPreview,receivedDateTime,sentDateTime,isRead,hasAttachments,importance,flag',
+    });
+    
+    if (filter) {
+      params.append('$filter', filter);
+    }
+    
+    url += `?${params.toString()}`;
+    
+    const response = await client.get(url);
+    
+    return response.data;
+  } catch (error: any) {
+    logger.error('Error fetching emails from Microsoft Graph', {
+      mailCredentialId,
+      folderId,
+      error: error instanceof Error ? error.message : String(error),
+      status: error.response?.status,
+      statusText: error.response?.statusText,
+    });
+    
+    // Check for authentication errors
+    if (error.response?.status === 401 || error.response?.status === 403) {
+      throw new Error('Microsoft Graph API access denied - may need to re-authenticate with Mail.Read and Mail.Send permissions');
+    }
+    
+    throw error;
+  }
+}
+
+/**
+ * Fetch a single email by ID from Microsoft Graph
+ */
+export async function fetchGraphEmail(
+  mailCredentialId: string,
+  messageId: string
+): Promise<GraphMailMessage> {
+  try {
+    const client = await getMicrosoftGraphClient(mailCredentialId);
+    
+    const response = await client.get(`/me/messages/${messageId}`, {
+      params: {
+        '$select': 'id,subject,from,toRecipients,ccRecipients,bccRecipients,body,bodyPreview,receivedDateTime,sentDateTime,isRead,hasAttachments,importance,flag,attachments',
+      },
+    });
+    
+    return response.data;
+  } catch (error: any) {
+    logger.error('Error fetching email from Microsoft Graph', {
+      mailCredentialId,
+      messageId,
+      error: error instanceof Error ? error.message : String(error),
+    });
+    
+    if (error.response?.status === 401 || error.response?.status === 403) {
+      throw new Error('Microsoft Graph API access denied - may need to re-authenticate with Mail.Read permissions');
+    }
+    
+    throw error;
+  }
+}
+
+/**
+ * Get list of mail folders from Microsoft Graph
+ */
+export async function fetchGraphMailFolders(
+  mailCredentialId: string
+): Promise<GraphMailFolder[]> {
+  try {
+    const client = await getMicrosoftGraphClient(mailCredentialId);
+    
+    const response = await client.get('/me/mailFolders', {
+      params: {
+        '$select': 'id,displayName,parentFolderId,childFolderCount,unreadItemCount,totalItemCount',
+        '$top': 100,
+      },
+    });
+    
+    return response.data.value || [];
+  } catch (error: any) {
+    logger.error('Error fetching mail folders from Microsoft Graph', {
+      mailCredentialId,
+      error: error instanceof Error ? error.message : String(error),
+    });
+    
+    if (error.response?.status === 401 || error.response?.status === 403) {
+      throw new Error('Microsoft Graph API access denied - may need to re-authenticate with Mail.Read permissions');
+    }
+    
+    throw error;
+  }
+}
+
+/**
+ * Send an email using Microsoft Graph API
+ */
+export async function sendGraphEmail(
+  mailCredentialId: string,
+  emailData: {
+    to: string | string[];
+    cc?: string | string[];
+    bcc?: string | string[];
+    subject: string;
+    body: string;
+    bodyType?: 'text' | 'html';
+    attachments?: Array<{
+      name: string;
+      content: string;
+      contentType: string;
+    }>;
+  }
+): Promise<{ id: string }> {
+  try {
+    const client = await getMicrosoftGraphClient(mailCredentialId);
+    
+    // Get the mail credential to get the sender email
+    const mailCredential = await prisma.mailCredentials.findUnique({
+      where: { id: mailCredentialId },
+      select: { email: true },
+    });
+    
+    if (!mailCredential) {
+      throw new Error('Mail credential not found');
+    }
+    
+    // Build the message payload
+    const message: any = {
+      subject: emailData.subject,
+      body: {
+        contentType: emailData.bodyType || 'html',
+        content: emailData.body,
+      },
+      toRecipients: Array.isArray(emailData.to)
+        ? emailData.to.map(email => ({ emailAddress: { address: email } }))
+        : [{ emailAddress: { address: emailData.to } }],
+    };
+    
+    if (emailData.cc) {
+      message.ccRecipients = Array.isArray(emailData.cc)
+        ? emailData.cc.map(email => ({ emailAddress: { address: email } }))
+        : [{ emailAddress: { address: emailData.cc } }];
+    }
+    
+    if (emailData.bcc) {
+      message.bccRecipients = Array.isArray(emailData.bcc)
+        ? emailData.bcc.map(email => ({ emailAddress: { address: email } }))
+        : [{ emailAddress: { address: emailData.bcc } }];
+    }
+    
+    if (emailData.attachments && emailData.attachments.length > 0) {
+      message.attachments = emailData.attachments.map(att => ({
+        '@odata.type': '#microsoft.graph.fileAttachment',
+        name: att.name,
+        contentType: att.contentType,
+        contentBytes: att.content, // Should be base64 encoded
+      }));
+    }
+    
+    // Create a draft message first to get the message ID
+    const draftResponse = await client.post('/me/messages', message);
+    const draftId = draftResponse.data.id;
+    
+    // Send the draft
+    await client.post(`/me/messages/${draftId}/send`);
+    
+    return { id: draftId };
+  } catch (error: any) {
+    logger.error('Error sending email via Microsoft Graph', {
+      mailCredentialId,
+      error: error instanceof Error ? error.message : String(error),
+      status: error.response?.status,
+      statusText: error.response?.statusText,
+    });
+    
+    if (error.response?.status === 401 || error.response?.status === 403) {
+      throw new Error('Microsoft Graph API access denied - may need to re-authenticate with Mail.Send permissions');
+    }
+    
+    throw error;
+  }
+}
+
+/**
+ * Mark an email as read/unread using Graph API
+ */
+export async function markGraphEmailAsRead(
+  mailCredentialId: string,
+  messageId: string,
+  isRead: boolean = true
+): Promise<void> {
+  try {
+    const client = await getMicrosoftGraphClient(mailCredentialId);
+    
+    await client.patch(`/me/messages/${messageId}`, {
+      isRead,
+    });
+  } catch (error: any) {
+    logger.error('Error marking email as read via Microsoft Graph', {
+      mailCredentialId,
+      messageId,
+      isRead,
+      error: error instanceof Error ? error.message : String(error),
+    });
+    
+    throw error;
+  }
+}
+
+/**
+ * Get unread email count for a folder
+ */
+export async function getGraphUnreadCount(
+  mailCredentialId: string,
+  folderId: string = 'Inbox'
+): Promise<number> {
+  try {
+    const client = await getMicrosoftGraphClient(mailCredentialId);
+    
+    const response = await client.get(`/me/mailFolders/${folderId}`, {
+      params: {
+        '$select': 'unreadItemCount',
+      },
+    });
+    
+    return response.data.unreadItemCount || 0;
+  } catch (error: any) {
+    logger.error('Error getting unread count from Microsoft Graph', {
+      mailCredentialId,
+      folderId,
+      error: error instanceof Error ? error.message : String(error),
+    });
+    
+    throw error;
+  }
+}
diff --git a/lib/services/microsoft-oauth.ts b/lib/services/microsoft-oauth.ts
index ad148f9..172e400 100644
--- a/lib/services/microsoft-oauth.ts
+++ b/lib/services/microsoft-oauth.ts
@@ -14,12 +14,13 @@ const redirectUri = process.env.MICROSOFT_REDIRECT_URI;
 
 // NOTE: In production we do not log Microsoft OAuth configuration to avoid noise and potential leakage.
 
-// Required scopes for IMAP, SMTP, and Calendar access
+// Required scopes for Microsoft Graph API (Mail and Calendar)
+// All scopes use the same resource (graph.microsoft.com) to avoid multi-resource errors
 const REQUIRED_SCOPES = [
   'offline_access',
-  'https://outlook.office.com/IMAP.AccessAsUser.All',
-  'https://outlook.office.com/SMTP.Send',
-  'https://graph.microsoft.com/Calendars.Read', // Microsoft Graph API scope for calendar read access
+  'https://graph.microsoft.com/Mail.Read',        // Read mail via Graph API
+  'https://graph.microsoft.com/Mail.Send',        // Send mail via Graph API
+  'https://graph.microsoft.com/Calendars.Read',   // Read calendars via Graph API
 ].join(' ');
 
 /**