diff --git a/server/db.ts b/server/db.ts
index da76716..b703efa 100644
--- a/server/db.ts
+++ b/server/db.ts
@@ -1221,3 +1221,18 @@ export async function updateWebImportSourceStatus(
   if (success) update.lastSuccessAt = new Date();
   await db.update(webImportSources).set(update).where(eq(webImportSources.id, id));
 }
+
+/**
+ * Check if a source file with the same fileName already exists for this user
+ * Used to prevent duplicate file storage during email import
+ */
+export async function findSourceFileByFileName(userId: number, fileName: string): Promise<any | null> {
+  const result = await db.select()
+    .from(sourceFiles)
+    .where(and(
+      eq(sourceFiles.userId, userId),
+      eq(sourceFiles.fileName, fileName)
+    ))
+    .limit(1);
+  return result[0] || null;
+}
diff --git a/server/emailImportService.ts b/server/emailImportService.ts
index dada7ce..0774dc8 100644
--- a/server/emailImportService.ts
+++ b/server/emailImportService.ts
@@ -9,6 +9,7 @@ import {
   isInvoiceBlacklisted,
   createInvoice,
   createImportLog,
+  findSourceFileByFileName,
 } from "./db";
 import { extractInvoicesWithMistral, generateMetadataJSON } from "./invoiceExtractor";
 import { localStoragePut, generateStorageKey } from "./localStorage";
@@ -32,6 +33,8 @@ interface EmailImportConfig {
 
 // Store active intervals for each user
 const activeIntervals = new Map<number, NodeJS.Timeout>();
+// Verrou anti-concurrence par userId
+const runningChecks = new Set<number>();
 
 /**
  * Process a single email attachment (PDF)
@@ -51,6 +54,12 @@ async function processEmailAttachment(
     console.log(`[EmailImport] File size: ${fileBuffer.length} bytes`);
     
     // Store source file
+    // ANTI-DUPLICATION
+    const existingSourceFile = await findSourceFileByFileName(userId, fileName);
+    if (existingSourceFile) {
+      console.log(`[EmailImport] File ${fileName} already imported for user ${userId}, skipping`);
+      return { success: true, totalInvoices: 0, imported: 0, duplicates: 1, errors: 0 };
+    }
     const sourceFileKey = generateStorageKey(userId, fileName);
     console.log(`[EmailImport] Generated storage key: ${sourceFileKey}`);
     
@@ -330,6 +339,12 @@ async function buildImapConfig(config: EmailImportConfig): Promise<Imap.Config>
  * Connect to IMAP and process unread emails with PDF attachments
  */
 async function checkEmailsForPDFs(config: EmailImportConfig): Promise<void> {
+  // Anti-concurrence
+  if (runningChecks.has(config.userId)) {
+    console.log(`[EmailImport] Check already running for user ${config.userId}, skipping`);
+    return;
+  }
+  runningChecks.add(config.userId);
   // Build IMAP config (may involve async OAuth2 token fetch)
   const imapConfig = await buildImapConfig(config);
 
@@ -380,7 +395,7 @@ async function checkEmailsForPDFs(config: EmailImportConfig): Promise<void> {
 
           const fetch = imap.fetch(results, {
             bodies: "",
-            markSeen: false, // Don't mark as seen yet
+            markSeen: true, // Mark as seen immediately to prevent re-processing
           });
 
           const processedEmails: number[] = [];
@@ -474,11 +489,13 @@ async function checkEmailsForPDFs(config: EmailImportConfig): Promise<void> {
     });
 
     imap.once("error", (err) => {
+      runningChecks.delete(config.userId);
       console.error("[EmailImport] IMAP connection error:", err);
       reject(err);
     });
 
     imap.once("end", () => {
+      runningChecks.delete(config.userId);
       console.log(`[EmailImport] IMAP connection ended for user ${config.userId}`);
     });