diff --git a/lib/services/email-service.ts b/lib/services/email-service.ts
index 1606594..7e1c49f 100644
--- a/lib/services/email-service.ts
+++ b/lib/services/email-service.ts
@@ -982,7 +982,9 @@ export async function getEmails(
           totalPages: Math.ceil(totalEmails / perPage),
           folder,
           mailboxes,
-          newestEmailId: emails.length > 0 ? parseInt(emails[0].id) || 0 : 0,
+          // For Graph API, IDs are strings, so we can't use parseInt
+          // Use a hash or just use the first email's ID as string, then convert to number if needed
+          newestEmailId: emails.length > 0 ? (emails[0].id.match(/^\d+$/) ? parseInt(emails[0].id) : 0) : 0,
         };
         
         // Cache the result
@@ -1219,6 +1221,7 @@ function mapAddresses(addresses: any[] | undefined): Array<{ name: string; addre
 
 /**
  * Get a single email with full content
+ * Supports both IMAP (numeric UIDs) and Microsoft Graph API (string IDs)
  */
 export async function getEmailContent(
   userId: string,
@@ -1231,17 +1234,6 @@ export async function getEmailContent(
     throw new Error('Missing required parameters');
   }
 
-  // Validate UID format
-  if (!/^\d+$/.test(emailId)) {
-    throw new Error('Invalid email ID format: must be a numeric UID');
-  }
-
-  // Convert to number for IMAP
-  const numericId = parseInt(emailId, 10);
-  if (isNaN(numericId)) {
-    throw new Error('Email ID must be a number');
-  }
-
   // Extract account ID from folder name if present and none was explicitly provided
   const folderAccountId = folder.includes(':') ? folder.split(':')[0] : accountId;
   
@@ -1258,6 +1250,99 @@ export async function getEmailContent(
     accountId: effectiveAccountId,
   });
   
+  // Check if this is a Microsoft account that should use Graph API
+  // Graph API uses string IDs (not numeric UIDs), so if emailId is not numeric, it's likely Graph
+  const isGraphId = !/^\d+$/.test(emailId);
+  const graphCheck = await shouldUseGraphAPI(userId, effectiveAccountId);
+  
+  if (isGraphId && graphCheck.useGraph && graphCheck.mailCredentialId) {
+    // Use Microsoft Graph API for Microsoft accounts with Graph IDs
+    logger.debug('[EMAIL] Fetching email content via Microsoft Graph API', {
+      userId,
+      emailId,
+      mailCredentialId: graphCheck.mailCredentialId,
+    });
+    
+    try {
+      // Use normalized folder name and effective account ID for cache key
+      const cachedEmail = await getCachedEmailContent(userId, effectiveAccountId, emailId);
+      if (cachedEmail) {
+        logger.debug('[EMAIL] Using cached email content (Graph)', {
+          userId,
+          accountId: effectiveAccountId,
+          emailId,
+        });
+        return cachedEmail;
+      }
+      
+      // Fetch from Graph API
+      const { fetchGraphEmail } = await import('./microsoft-graph-mail');
+      const graphMessage = await fetchGraphEmail(graphCheck.mailCredentialId, emailId);
+      
+      // Convert Graph message to EmailMessage format
+      const email: EmailMessage = {
+        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,
+          draft: false,
+          deleted: false,
+        },
+        size: 0,
+        hasAttachments: graphMessage.hasAttachments || false,
+        folder: normalizedFolder,
+        contentFetched: true,
+        accountId: effectiveAccountId,
+        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,
+      };
+      
+      // Cache the email content
+      await cacheEmailContent(userId, effectiveAccountId, emailId, email);
+      
+      return email;
+    } catch (error) {
+      logger.error('[EMAIL] Error fetching email content from Graph API', {
+        userId,
+        emailId,
+        error: error instanceof Error ? error.message : String(error),
+      });
+      throw error;
+    }
+  }
+  
+  // Use IMAP for non-Microsoft accounts or numeric UIDs
+  // Validate UID format for IMAP
+  if (!/^\d+$/.test(emailId)) {
+    throw new Error('Invalid email ID format: must be a numeric UID for IMAP accounts');
+  }
+
+  // Convert to number for IMAP
+  const numericId = parseInt(emailId, 10);
+  if (isNaN(numericId)) {
+    throw new Error('Email ID must be a number for IMAP accounts');
+  }
+  
   // Use normalized folder name and effective account ID for cache key
   const cachedEmail = await getCachedEmailContent(userId, effectiveAccountId, emailId);
   if (cachedEmail) {
@@ -1441,6 +1526,7 @@ export async function getEmailContent(
 
 /**
  * Mark an email as read or unread
+ * Supports both IMAP (numeric UIDs) and Microsoft Graph API (string IDs)
  */
 export async function markEmailReadStatus(
   userId: string,
@@ -1466,6 +1552,41 @@ export async function markEmailReadStatus(
     accountId: effectiveAccountId,
   });
   
+  // Check if this is a Microsoft account that should use Graph API
+  // Graph API uses string IDs (not numeric UIDs), so if emailId is not numeric, it's likely Graph
+  const isGraphId = !/^\d+$/.test(emailId);
+  const graphCheck = await shouldUseGraphAPI(userId, effectiveAccountId);
+  
+  if (isGraphId && graphCheck.useGraph && graphCheck.mailCredentialId) {
+    // Use Microsoft Graph API for Microsoft accounts with Graph IDs
+    logger.debug('[EMAIL] Marking email as read/unread via Microsoft Graph API', {
+      userId,
+      emailId,
+      isRead,
+      mailCredentialId: graphCheck.mailCredentialId,
+    });
+    
+    try {
+      const { markGraphEmailAsRead } = await import('./microsoft-graph-mail');
+      await markGraphEmailAsRead(graphCheck.mailCredentialId, emailId, isRead);
+      return true;
+    } catch (error) {
+      logger.error('[EMAIL] Error marking email as read/unread via Graph API', {
+        userId,
+        emailId,
+        isRead,
+        error: error instanceof Error ? error.message : String(error),
+      });
+      return false;
+    }
+  }
+  
+  // Use IMAP for non-Microsoft accounts or numeric UIDs
+  // Validate UID format for IMAP
+  if (!/^\d+$/.test(emailId)) {
+    throw new Error('Invalid email ID format: must be a numeric UID for IMAP accounts');
+  }
+  
   const client = await getImapConnection(userId, effectiveAccountId);
   
   try {