diff --git a/apps/api/src/dkv/dkv.controller.ts b/apps/api/src/dkv/dkv.controller.ts
index fb7e798..391fe2d 100644
--- a/apps/api/src/dkv/dkv.controller.ts
+++ b/apps/api/src/dkv/dkv.controller.ts
@@ -55,12 +55,16 @@ export class DkvController {
 
   // ─── Config ────────────────────────────────────────────────────────────────
 
-  /** GET /dkv/config — returns module config without encrypted credentials. */
+  /** GET /dkv/config — returns module config without encrypted credentials. 404 when not yet configured. */
   @Get('config')
   @Roles(Role.ADMIN, Role.SUPER_ADMIN)
   async getConfig(@Req() req: any) {
     const tenantId = this._requireTenant(req);
-    return this.dkvService.loadConfig(tenantId);
+    const config = await this.dkvService.loadConfig(tenantId);
+    if (!config) {
+      throw new NotFoundException('DKV module not yet configured');
+    }
+    return config;
   }
 
   /**
diff --git a/apps/api/src/dkv/providers/imap.provider.ts b/apps/api/src/dkv/providers/imap.provider.ts
index 893fd78..ae17abf 100644
--- a/apps/api/src/dkv/providers/imap.provider.ts
+++ b/apps/api/src/dkv/providers/imap.provider.ts
@@ -56,11 +56,19 @@ function collectPdfParts(
 ): string[] {
   if (!node) return parts;
 
-  // Check this node — type is the full MIME type (e.g. "application/pdf")
-  if (
-    node.type?.toLowerCase() === 'application/pdf' &&
-    node.part !== undefined
-  ) {
+  const type = node.type?.toLowerCase() ?? '';
+  // Some mail clients (e.g. Outlook) send PDFs as application/octet-stream.
+  // Fall back to checking the filename from Content-Disposition or Content-Type parameters.
+  const dispositionFilename =
+    ((node as any).disposition?.parameters?.filename as string | undefined)?.toLowerCase() ?? '';
+  const typeFilename =
+    ((node as any).parameters?.name as string | undefined)?.toLowerCase() ?? '';
+  const looksLikePdf =
+    type === 'application/pdf' ||
+    (type === 'application/octet-stream' &&
+      (dispositionFilename.endsWith('.pdf') || typeFilename.endsWith('.pdf')));
+
+  if (looksLikePdf && node.part !== undefined) {
     parts.push(node.part);
   }
 
@@ -112,10 +120,12 @@ export class ImapProvider implements InboxProvider {
 
     try {
       lock = await client.getMailboxLock(config.folder || 'INBOX');
-      // Search for emails from the configured sender
-      const searchQuery = config.senderFilter
-        ? { from: config.senderFilter }
-        : {};
+      // Search only UNSEEN emails to avoid reprocessing already-handled messages.
+      // Combine with sender filter when configured.
+      const searchQuery: Record<string, unknown> = { seen: false };
+      if (config.senderFilter) {
+        searchQuery.from = config.senderFilter;
+      }
       const uids = await client.search(searchQuery, { uid: true });
 
       if (!uids || uids.length === 0) {
@@ -171,6 +181,12 @@ export class ImapProvider implements InboxProvider {
             date: msg.envelope?.date ?? new Date(),
             attachments,
           });
+          // Mark as read so subsequent polls skip this message (UNSEEN filter above).
+          try {
+            await client.messageFlagsAdd(String(msg.uid), ['\\Seen'], { uid: true });
+          } catch {
+            // Non-fatal: message will simply appear again on next poll
+          }
         }
       }
     } finally {
diff --git a/apps/web/src/app/(portal)/modules/dkv-fleet/settings/components/InboxConfigForm.tsx b/apps/web/src/app/(portal)/modules/dkv-fleet/settings/components/InboxConfigForm.tsx
index c865bc3..65d4145 100644
--- a/apps/web/src/app/(portal)/modules/dkv-fleet/settings/components/InboxConfigForm.tsx
+++ b/apps/web/src/app/(portal)/modules/dkv-fleet/settings/components/InboxConfigForm.tsx
@@ -4,6 +4,7 @@ import { useCallback, useEffect, useState } from 'react';
 import { useTranslations } from 'next-intl';
 import {
   type DkvConfig,
+  checkNow,
   fetchConfig,
   saveConfig,
   testConnection,
@@ -154,14 +155,24 @@ export function InboxConfigForm() {
   const [saveError, setSaveError] = useState<string | null>(null);
   const [saveSuccess, setSaveSuccess] = useState(false);
 
+  // Check-now state
+  const [isChecking, setIsChecking] = useState(false);
+  const [checkResult, setCheckResult] = useState<{ status: string; message: string } | null>(null);
+
+  // Whether config exists in DB (null = not yet saved)
+  const [configExists, setConfigExists] = useState(false);
+
   // Load config on mount
   useEffect(() => {
     fetchConfig()
       .then((config) => {
-        setForm(configToForm(config));
+        if (config) {
+          setForm(configToForm(config));
+          setConfigExists(true);
+        }
       })
       .catch(() => {
-        // Keep defaults if config not yet created
+        // Keep defaults if fetch failed
       })
       .finally(() => {
         setIsLoading(false);
@@ -201,6 +212,7 @@ export function InboxConfigForm() {
     try {
       await saveConfig(formToPayload(form));
       setSaveSuccess(true);
+      setConfigExists(true);
       // Clear password field after save (T-07-12)
       setForm((f) => ({ ...f, password: '' }));
     } catch (err) {
@@ -212,6 +224,22 @@ export function InboxConfigForm() {
     }
   };
 
+  const handleCheckNow = async () => {
+    setIsChecking(true);
+    setCheckResult(null);
+    try {
+      const result = await checkNow();
+      setCheckResult(result);
+    } catch (err) {
+      setCheckResult({
+        status: 'error',
+        message: err instanceof Error ? err.message : 'Fehler beim Abrufen',
+      });
+    } finally {
+      setIsChecking(false);
+    }
+  };
+
   const inputCls =
     'h-9 w-full max-w-md rounded border border-border bg-background px-3 text-sm text-foreground';
   const labelCls = 'mb-1 block text-sm text-foreground';
@@ -231,6 +259,12 @@ export function InboxConfigForm() {
 
   return (
     <div className="space-y-4">
+      {/* Banner: config not yet saved */}
+      {!configExists && (
+        <div className="rounded-md border border-amber-300 bg-amber-50 px-4 py-3 text-sm text-amber-800 dark:border-amber-700 dark:bg-amber-900/20 dark:text-amber-300">
+          Noch nicht gespeichert — Konfiguration ausfüllen und speichern.
+        </div>
+      )}
       {/* Protokoll */}
       <div>
         <label htmlFor="dkv-protocol" className={labelCls}>
@@ -503,8 +537,28 @@ export function InboxConfigForm() {
         >
           {t('form.save')}
         </button>
+        {configExists && (
+          <button
+            type="button"
+            onClick={handleCheckNow}
+            disabled={isChecking || isSaving || isTesting}
+            className="rounded border border-border px-4 py-2 text-sm text-foreground transition-colors hover:bg-muted disabled:opacity-50 disabled:cursor-not-allowed"
+          >
+            {isChecking ? 'Prüfe...' : 'Jetzt prüfen'}
+          </button>
+        )}
       </div>
 
+      {/* Check-now result */}
+      {checkResult && (
+        <p
+          className="text-sm"
+          style={{ color: checkResult.status === 'ok' ? 'oklch(0.40 0.15 148)' : 'var(--destructive)' }}
+        >
+          {checkResult.status === 'ok' ? `✓ ${checkResult.message}` : `✗ ${checkResult.message}`}
+        </p>
+      )}
+
       {/* Inline test feedback */}
       {testResult !== null && (
         <div className="space-y-1">
diff --git a/apps/web/src/lib/dkv-api.ts b/apps/web/src/lib/dkv-api.ts
index 60c60ce..682b9a0 100644
--- a/apps/web/src/lib/dkv-api.ts
+++ b/apps/web/src/lib/dkv-api.ts
@@ -95,10 +95,11 @@ export interface DkvHistoryPage {
  * Fetch the current DKV module inbox configuration.
  * GET /dkv/config
  */
-export async function fetchConfig(): Promise<DkvConfig> {
+export async function fetchConfig(): Promise<DkvConfig | null> {
   const res = await fetch(`${API_URL}/dkv/config`, {
     credentials: 'include',
   });
+  if (res.status === 404) return null;
   if (!res.ok) throw new Error('Failed to fetch DKV config');
   return res.json();
 }
@@ -143,12 +144,13 @@ export async function testConnection(
  * Trigger an immediate inbox check (manual poll).
  * POST /dkv/check-now
  */
-export async function checkNow(): Promise<void> {
+export async function checkNow(): Promise<{ status: string; message: string; checkedAt: string }> {
   const res = await fetch(`${API_URL}/dkv/check-now`, {
     method: 'POST',
     credentials: 'include',
   });
   if (!res.ok) throw new Error('Failed to trigger DKV inbox check');
+  return res.json();
 }
 
 /**