diff --git a/app/agenda/page.tsx b/app/agenda/page.tsx
index 2876c8c..f5d80f4 100644
--- a/app/agenda/page.tsx
+++ b/app/agenda/page.tsx
@@ -556,6 +556,35 @@ export default async function CalendarPage() {
     }
   }
 
+  // Auto-sync Microsoft calendars if needed (background, don't block page load)
+  const microsoftSyncConfigs = await prisma.calendarSync.findMany({
+    where: {
+      provider: 'microsoft',
+      syncEnabled: true,
+      calendar: {
+        userId: session?.user?.id || ''
+      }
+    }
+  });
+
+  // Trigger sync for Microsoft calendars that need it (async, don't wait)
+  for (const syncConfig of microsoftSyncConfigs) {
+    const needsSync = !syncConfig.lastSyncAt || 
+      (Date.now() - syncConfig.lastSyncAt.getTime()) / (1000 * 60) >= syncConfig.syncFrequency;
+    
+    if (needsSync) {
+      // Trigger sync in background (don't await to avoid blocking page load)
+      import('@/lib/services/microsoft-calendar-sync').then(({ syncMicrosoftCalendar }) => {
+        syncMicrosoftCalendar(syncConfig.id, false).catch((error) => {
+          console.error('Background sync failed for Microsoft calendar', {
+            calendarSyncId: syncConfig.id,
+            error: error instanceof Error ? error.message : String(error),
+          });
+        });
+      });
+    }
+  }
+
   // Refresh calendars after auto-setup and cleanup
   // Exclude "Privée" and "Default" calendars that are not synced
   // IMPORTANT: Include all "Privée"/"Default" calendars that have ANY syncConfig (enabled or disabled)
diff --git a/components/calendar/calendar-client.tsx b/components/calendar/calendar-client.tsx
index d313320..9bbf3f5 100644
--- a/components/calendar/calendar-client.tsx
+++ b/components/calendar/calendar-client.tsx
@@ -680,8 +680,8 @@ function EventPreview({ event, calendar }: { event: Event; calendar: Calendar })
 
       {isExpanded && (
         <div className="space-y-4">
-          {event.description && (
-            <p className="text-sm text-gray-600">{event.description}</p>
+          {cleanDescription(event.description) && (
+            <p className="text-sm text-gray-600">{cleanDescription(event.description)}</p>
           )}
 
           <div className="space-y-2">
@@ -995,7 +995,7 @@ export function CalendarClient({ initialCalendars, userId, userProfile }: Calend
     setSelectedEvent(event.extendedProps.originalEvent);
     setEventForm({
       title: event.title,
-      description: event.extendedProps.description,
+      description: cleanDescription(event.extendedProps.description),
       start: startDate.toISOString().slice(0, 16),
       end: endDate.toISOString().slice(0, 16),
       allDay: event.isAllDay,
@@ -1148,6 +1148,14 @@ export function CalendarClient({ initialCalendars, userId, userProfile }: Calend
     }
   };
 
+  // Helper function to clean description by removing Microsoft ID prefix
+  const cleanDescription = (description: string | null | undefined): string | null => {
+    if (!description) return null;
+    // Remove [MS_ID:xxx] prefix if present
+    const cleaned = description.replace(/^\[MS_ID:[^\]]+\]\n?/, '');
+    return cleaned.trim() || null;
+  };
+
   const getCalendarDisplayName = (calendar: CalendarWithMission) => {
     // If calendar is synced to an external account, use the same display name as in courrier
     if (calendar.syncConfig?.syncEnabled && calendar.syncConfig?.mailCredential) {
@@ -1465,7 +1473,7 @@ export function CalendarClient({ initialCalendars, userId, userProfile }: Calend
                   start: new Date(event.start),
                   end: new Date(event.end),
                 allDay: event.isAllDay,
-                  description: event.description,
+                  description: cleanDescription(event.description),
                   location: event.location,
                   calendarId: event.calendarId,
                   backgroundColor: `${cal.color}dd`,
@@ -1474,7 +1482,7 @@ export function CalendarClient({ initialCalendars, userId, userProfile }: Calend
                   extendedProps: {
                     calendarName: cal.name,
                     location: event.location,
-                    description: event.description,
+                    description: cleanDescription(event.description),
                     calendarId: event.calendarId,
                     originalEvent: event,
                     color: cal.color
diff --git a/lib/services/microsoft-calendar-sync.ts b/lib/services/microsoft-calendar-sync.ts
index 7b4c7e1..351277c 100644
--- a/lib/services/microsoft-calendar-sync.ts
+++ b/lib/services/microsoft-calendar-sync.ts
@@ -288,16 +288,32 @@ export async function syncMicrosoftCalendar(
 
     // Sync events: create or update
     for (const caldavEvent of caldavEvents) {
-      // Try to find existing event by matching title and start date
-      const existingEvent = existingEvents.find(
-        (e) =>
-          e.title === caldavEvent.summary &&
-          Math.abs(new Date(e.start).getTime() - caldavEvent.start.getTime()) < 60000 // Within 1 minute
-      );
+      // Store Microsoft ID in description with a special prefix for matching
+      const microsoftId = caldavEvent.uid;
+      const descriptionWithId = caldavEvent.description 
+        ? `[MS_ID:${microsoftId}]\n${caldavEvent.description}`
+        : `[MS_ID:${microsoftId}]`;
+
+      // Try to find existing event by Microsoft ID first (most reliable)
+      let existingEvent = existingEvents.find((e) => {
+        if (e.description && e.description.includes(`[MS_ID:${microsoftId}]`)) {
+          return true;
+        }
+        return false;
+      });
+
+      // Fallback: try to find by matching title and start date (for events created before this fix)
+      if (!existingEvent) {
+        existingEvent = existingEvents.find(
+          (e) =>
+            e.title === caldavEvent.summary &&
+            Math.abs(new Date(e.start).getTime() - caldavEvent.start.getTime()) < 60000 // Within 1 minute
+        );
+      }
 
       const eventData = {
         title: caldavEvent.summary,
-        description: caldavEvent.description || null,
+        description: descriptionWithId,
         start: caldavEvent.start,
         end: caldavEvent.end,
         location: caldavEvent.location || null,