diff --git a/.eslintrc.json b/.eslintrc.json
new file mode 100644
index 0000000..bffb357
--- /dev/null
+++ b/.eslintrc.json
@@ -0,0 +1,3 @@
+{
+  "extends": "next/core-web-vitals"
+}
diff --git a/src/app/api/campaigns/[id]/route.ts b/src/app/api/campaigns/[id]/route.ts
index 538eead..7d28135 100644
--- a/src/app/api/campaigns/[id]/route.ts
+++ b/src/app/api/campaigns/[id]/route.ts
@@ -1,14 +1,14 @@
 import { NextRequest, NextResponse } from 'next/server'
 import { UpdateCampaignSchema } from '../../../../lib/validation'
 import { getCampaign, updateCampaign } from '../../../../server/db/campaigns'
-
-function getTenantId(req: NextRequest): string {
-  return req.headers.get('x-tenant-id') ?? 'default'
-}
+import { getTenantId } from '../../../../lib/tenant-header'
 
 export async function GET(req: NextRequest, { params }: { params: { id: string } }) {
   const result = await getCampaign(getTenantId(req), params.id)
-  if (!result.ok) return NextResponse.json({ error: result.error.message }, { status: 404 })
+  if (!result.ok) {
+    const status = result.error.message.includes('nicht gefunden') ? 404 : 500
+    return NextResponse.json({ error: result.error.message }, { status })
+  }
   return NextResponse.json(result.data)
 }
 
@@ -18,6 +18,9 @@ export async function PATCH(req: NextRequest, { params }: { params: { id: string
   const parsed = UpdateCampaignSchema.safeParse(body)
   if (!parsed.success) return NextResponse.json({ error: parsed.error.issues }, { status: 400 })
   const result = await updateCampaign(tenantId, params.id, parsed.data)
-  if (!result.ok) return NextResponse.json({ error: result.error.message }, { status: 400 })
+  if (!result.ok) {
+    const status = result.error.message.includes('nicht gefunden') ? 404 : 400
+    return NextResponse.json({ error: result.error.message }, { status })
+  }
   return NextResponse.json(result.data)
 }
diff --git a/src/app/api/campaigns/[id]/schedule/route.ts b/src/app/api/campaigns/[id]/schedule/route.ts
index 3523cbd..63dac82 100644
--- a/src/app/api/campaigns/[id]/schedule/route.ts
+++ b/src/app/api/campaigns/[id]/schedule/route.ts
@@ -1,10 +1,7 @@
 import { NextRequest, NextResponse } from 'next/server'
 import { ScheduleCampaignSchema } from '../../../../../lib/validation'
-import { updateCampaignStatus } from '../../../../../server/db/campaigns'
-
-function getTenantId(req: NextRequest): string {
-  return req.headers.get('x-tenant-id') ?? 'default'
-}
+import { getCampaign, updateCampaignStatus } from '../../../../../server/db/campaigns'
+import { getTenantId } from '../../../../../lib/tenant-header'
 
 export async function POST(req: NextRequest, { params }: { params: { id: string } }) {
   const tenantId = getTenantId(req)
@@ -12,17 +9,26 @@ export async function POST(req: NextRequest, { params }: { params: { id: string
   const parsed = ScheduleCampaignSchema.safeParse(body)
   if (!parsed.success) return NextResponse.json({ error: parsed.error.issues }, { status: 400 })
 
+  // immediate-Typ gehört zur /send Route, nicht zu /schedule (Fix I4)
+  if (parsed.data.type === 'immediate') {
+    return NextResponse.json({ error: 'Für sofortigen Versand /send verwenden' }, { status: 400 })
+  }
+
+  // Draft-Status-Guard — nur Draft-Kampagnen können geplant werden (Fix I5)
+  const campaignResult = await getCampaign(tenantId, params.id)
+  if (!campaignResult.ok) return NextResponse.json({ error: campaignResult.error.message }, { status: 404 })
+  if (campaignResult.data.status !== 'draft') {
+    return NextResponse.json({ error: 'Nur Draft-Kampagnen können geplant werden' }, { status: 400 })
+  }
+
   const schedule = parsed.data
-  let scheduledAt: Date | undefined
-  let cronExpression: string | undefined
+  const scheduledAt = schedule.type === 'once' ? schedule.scheduledAt : undefined
+  const cronExpression = schedule.type === 'cron' ? schedule.cronExpression : undefined
 
-  if (schedule.type === 'once') scheduledAt = schedule.scheduledAt
-  if (schedule.type === 'cron') cronExpression = schedule.cronExpression
-
-  const result = await updateCampaignStatus(tenantId, params.id, 'scheduled', {
-    scheduledAt,
-    cronExpression,
-  })
-  if (!result.ok) return NextResponse.json({ error: result.error.message }, { status: 400 })
+  const result = await updateCampaignStatus(tenantId, params.id, 'scheduled', { scheduledAt, cronExpression })
+  if (!result.ok) {
+    const status = result.error.message.includes('nicht gefunden') ? 404 : 400
+    return NextResponse.json({ error: result.error.message }, { status })
+  }
   return NextResponse.json(result.data)
 }
diff --git a/src/app/api/campaigns/[id]/send/route.ts b/src/app/api/campaigns/[id]/send/route.ts
index 902961b..9030068 100644
--- a/src/app/api/campaigns/[id]/send/route.ts
+++ b/src/app/api/campaigns/[id]/send/route.ts
@@ -1,12 +1,10 @@
 import { NextRequest, NextResponse } from 'next/server'
 import { getCampaign, updateCampaignStatus } from '../../../../../server/db/campaigns'
-import { enqueueEmailSend } from '../../../../../queues/email-send.queue'
+import { emailSendQueue } from '../../../../../queues/email-send.queue'
 import { withTenant } from '../../../../../server/db/tenant'
 import { hashEmail } from '../../../../../lib/crypto'
-
-function getTenantId(req: NextRequest): string {
-  return req.headers.get('x-tenant-id') ?? 'default'
-}
+import { checkSuppression } from '../../../../../server/suppression/check'
+import { getTenantId } from '../../../../../lib/tenant-header'
 
 export async function POST(req: NextRequest, { params }: { params: { id: string } }) {
   const tenantId = getTenantId(req)
@@ -19,7 +17,11 @@ export async function POST(req: NextRequest, { params }: { params: { id: string
     return NextResponse.json({ error: 'Nur Draft-Kampagnen können versendet werden' }, { status: 400 })
   }
 
-  await updateCampaignStatus(tenantId, params.id, 'sending')
+  // Status auf 'sending' setzen — Ergebnis prüfen (Fix C1)
+  const statusResult = await updateCampaignStatus(tenantId, params.id, 'sending')
+  if (!statusResult.ok) {
+    return NextResponse.json({ error: statusResult.error.message }, { status: 500 })
+  }
 
   const recipients = await withTenant(tenantId, (client) =>
     client.query<{ email: string }>(
@@ -31,14 +33,32 @@ export async function POST(req: NextRequest, { params }: { params: { id: string
     )
   )
 
-  for (const recipient of recipients) {
-    await enqueueEmailSend({
-      tenantId,
-      campaignId: params.id,
-      recipientEmail: recipient.email,
-      recipientHash: hashEmail(recipient.email),
+  // Suppression-Check PFLICHT — kein Opt-out-Empfänger darf in die Queue (Fix C3)
+  const unsuppressedRecipients = await Promise.all(
+    recipients.map(async (r) => {
+      const suppressed = await checkSuppression(tenantId, r.email)
+      return suppressed ? null : r
     })
-  }
+  ).then((results) => results.filter((r): r is { email: string } => r !== null))
 
-  return NextResponse.json({ queued: recipients.length })
+  // Bulk-Enqueue — schnell, kein sequenzielles await (Fix C2)
+  const addedJobs = await emailSendQueue.addBulk(
+    unsuppressedRecipients.map((recipient) => ({
+      name: 'send',
+      data: {
+        tenantId,
+        campaignId: params.id,
+        recipientEmail: recipient.email,
+        recipientHash: hashEmail(recipient.email),
+      },
+      opts: {
+        attempts: 3,
+        backoff: { type: 'exponential' as const, delay: 2000 },
+        removeOnComplete: 100,
+        removeOnFail: { count: 500 },
+      },
+    }))
+  )
+
+  return NextResponse.json({ queued: addedJobs.length })
 }
diff --git a/src/app/api/campaigns/route.ts b/src/app/api/campaigns/route.ts
index 5ecc8a3..af67f68 100644
--- a/src/app/api/campaigns/route.ts
+++ b/src/app/api/campaigns/route.ts
@@ -1,10 +1,7 @@
 import { NextRequest, NextResponse } from 'next/server'
 import { CreateCampaignSchema } from '../../../lib/validation'
 import { createCampaign, listCampaigns } from '../../../server/db/campaigns'
-
-function getTenantId(req: NextRequest): string {
-  return req.headers.get('x-tenant-id') ?? 'default'
-}
+import { getTenantId } from '../../../lib/tenant-header'
 
 export async function GET(req: NextRequest) {
   const tenantId = getTenantId(req)
diff --git a/src/lib/tenant-header.ts b/src/lib/tenant-header.ts
new file mode 100644
index 0000000..6b5717b
--- /dev/null
+++ b/src/lib/tenant-header.ts
@@ -0,0 +1,5 @@
+import { NextRequest } from 'next/server'
+
+export function getTenantId(req: NextRequest): string {
+  return req.headers.get('x-tenant-id') ?? 'default'
+}