From f3384cfc741669e92824d96dcbdd68828d0717c9 Mon Sep 17 00:00:00 2001
From: florianfederspiel <florian@fedeo.de>
Date: Mon, 7 Sep 2026 19:00:08 +0200
Subject: [PATCH] =?UTF-8?q?KI-AGENT:=20Mailantworten=20und=20Entit=C3=A4ts?=
 =?UTF-8?q?verkn=C3=BCpfungen=20erg=C3=A4nzen?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../db/migrations/0066_email_entity_links.sql |  27 +++
 backend/db/migrations/meta/_journal.json      |   7 +
 backend/db/schema/emails.ts                   |  35 +++
 backend/src/routes/emailAsUser.ts             | 227 +++++++++++++++++-
 frontend/components/EntityShow.vue            |  10 +
 .../components/email/EmailEntityLinks.vue     | 169 +++++++++++++
 .../components/email/EmailEntityMessages.vue  | 129 ++++++++++
 frontend/pages/email/index.vue                |  59 ++++-
 frontend/pages/email/new.vue                  | 133 ++++++++--
 frontend/stores/data.js                       |   8 +-
 10 files changed, 774 insertions(+), 30 deletions(-)
 create mode 100644 backend/db/migrations/0066_email_entity_links.sql
 create mode 100644 frontend/components/email/EmailEntityLinks.vue
 create mode 100644 frontend/components/email/EmailEntityMessages.vue

diff --git a/backend/db/migrations/0066_email_entity_links.sql b/backend/db/migrations/0066_email_entity_links.sql
new file mode 100644
index 0000000..8fd43d7
--- /dev/null
+++ b/backend/db/migrations/0066_email_entity_links.sql
@@ -0,0 +1,27 @@
+CREATE TABLE IF NOT EXISTS "email_entity_links" (
+    "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+    "tenant_id" bigint NOT NULL,
+    "message_id" uuid NOT NULL,
+    "entity_type" text NOT NULL,
+    "entity_id" bigint NOT NULL,
+    "linked_by" uuid,
+    "created_at" timestamp with time zone DEFAULT now() NOT NULL,
+    CONSTRAINT "email_entity_links_tenant_id_tenants_id_fk"
+        FOREIGN KEY ("tenant_id") REFERENCES "public"."tenants"("id")
+        ON DELETE cascade ON UPDATE cascade,
+    CONSTRAINT "email_entity_links_message_id_email_messages_id_fk"
+        FOREIGN KEY ("message_id") REFERENCES "public"."email_messages"("id")
+        ON DELETE cascade ON UPDATE cascade,
+    CONSTRAINT "email_entity_links_linked_by_auth_users_id_fk"
+        FOREIGN KEY ("linked_by") REFERENCES "public"."auth_users"("id")
+        ON DELETE set null ON UPDATE cascade
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS "email_entity_links_message_entity_key"
+    ON "email_entity_links" USING btree ("message_id", "entity_type", "entity_id");
+
+CREATE INDEX IF NOT EXISTS "email_entity_links_entity_idx"
+    ON "email_entity_links" USING btree ("tenant_id", "entity_type", "entity_id");
+
+CREATE INDEX IF NOT EXISTS "email_entity_links_message_idx"
+    ON "email_entity_links" USING btree ("message_id");
diff --git a/backend/db/migrations/meta/_journal.json b/backend/db/migrations/meta/_journal.json
index 032bf0c..c8904de 100644
--- a/backend/db/migrations/meta/_journal.json
+++ b/backend/db/migrations/meta/_journal.json
@@ -442,6 +442,13 @@
       "when": 1788202715001,
       "tag": "0065_document_templates",
       "breakpoints": true
+    },
+    {
+      "idx": 63,
+      "version": "7",
+      "when": 1788799700000,
+      "tag": "0066_email_entity_links",
+      "breakpoints": true
     }
   ]
 }
diff --git a/backend/db/schema/emails.ts b/backend/db/schema/emails.ts
index 1a600eb..035c1cc 100644
--- a/backend/db/schema/emails.ts
+++ b/backend/db/schema/emails.ts
@@ -155,6 +155,39 @@ export const emailAttachments = pgTable(
     }),
 )
 
+export const emailEntityLinks = pgTable(
+    "email_entity_links",
+    {
+        id: uuid("id").primaryKey().defaultRandom(),
+
+        tenantId: bigint("tenant_id", { mode: "number" })
+            .notNull()
+            .references(() => tenants.id, { onDelete: "cascade", onUpdate: "cascade" }),
+
+        messageId: uuid("message_id")
+            .notNull()
+            .references(() => emailMessages.id, { onDelete: "cascade", onUpdate: "cascade" }),
+
+        entityType: text("entity_type").notNull(),
+        entityId: bigint("entity_id", { mode: "number" }).notNull(),
+
+        linkedBy: uuid("linked_by")
+            .references(() => authUsers.id, { onDelete: "set null", onUpdate: "cascade" }),
+
+        createdAt: timestamp("created_at", { withTimezone: true })
+            .notNull()
+            .defaultNow(),
+    },
+    (table) => ({
+        messageEntityKey: uniqueIndex("email_entity_links_message_entity_key")
+            .on(table.messageId, table.entityType, table.entityId),
+        entityIdx: index("email_entity_links_entity_idx")
+            .on(table.tenantId, table.entityType, table.entityId),
+        messageIdx: index("email_entity_links_message_idx")
+            .on(table.messageId),
+    }),
+)
+
 export const emailSyncState = pgTable(
     "email_sync_state",
     {
@@ -204,5 +237,7 @@ export type EmailMessageBody = typeof emailMessageBodies.$inferSelect
 export type NewEmailMessageBody = typeof emailMessageBodies.$inferInsert
 export type EmailAttachment = typeof emailAttachments.$inferSelect
 export type NewEmailAttachment = typeof emailAttachments.$inferInsert
+export type EmailEntityLink = typeof emailEntityLinks.$inferSelect
+export type NewEmailEntityLink = typeof emailEntityLinks.$inferInsert
 export type EmailSyncState = typeof emailSyncState.$inferSelect
 export type NewEmailSyncState = typeof emailSyncState.$inferInsert
diff --git a/backend/src/routes/emailAsUser.ts b/backend/src/routes/emailAsUser.ts
index 37e42e3..ff68692 100644
--- a/backend/src/routes/emailAsUser.ts
+++ b/backend/src/routes/emailAsUser.ts
@@ -1,9 +1,17 @@
 import nodemailer from "nodemailer"
 import { FastifyInstance } from "fastify"
-import { and, eq } from "drizzle-orm"
+import { and, desc, eq } from "drizzle-orm"
 
 import { encrypt, decrypt } from "../utils/crypt"
-import { userCredentials } from "../../db/schema"
+import {
+    customers,
+    emailEntityLinks,
+    emailMessages,
+    plants,
+    projects,
+    userCredentials,
+    vendors,
+} from "../../db/schema"
 import { emailSyncService } from "../modules/email/email.sync.service"
 
 // @ts-ignore
@@ -39,6 +47,53 @@ export default async function emailAsUserRoutes(server: FastifyInstance) {
 
     const bodyValue = (body: any, camelKey: string, snakeKey: string) => body[camelKey] ?? body[snakeKey]
 
+    const entityDefinitions = {
+        customers: { table: customers, tenantColumn: customers.tenant, labelColumn: customers.name, label: "Kunde" },
+        vendors: { table: vendors, tenantColumn: vendors.tenant, labelColumn: vendors.name, label: "Lieferant" },
+        projects: { table: projects, tenantColumn: projects.tenant, labelColumn: projects.name, label: "Projekt" },
+        plants: { table: plants, tenantColumn: plants.tenant, labelColumn: plants.name, label: "Objekt" },
+    } as const
+
+    type EmailEntityType = keyof typeof entityDefinitions
+
+    const getEntityDefinition = (entityType: string) =>
+        entityDefinitions[entityType as EmailEntityType] || null
+
+    const loadEntity = async (tenantId: number, entityType: string, entityId: number) => {
+        const definition = getEntityDefinition(entityType)
+        if (!definition) return null
+
+        const rows = await server.db
+            .select({ id: definition.table.id, name: definition.labelColumn })
+            .from(definition.table)
+            .where(and(
+                eq(definition.tenantColumn, tenantId),
+                eq(definition.table.id, entityId),
+            ))
+            .limit(1)
+
+        return rows[0] ? { ...rows[0], typeLabel: definition.label } : null
+    }
+
+    const listMessageEntityLinks = async (tenantId: number, messageId: string) => {
+        const links = await server.db
+            .select()
+            .from(emailEntityLinks)
+            .where(and(
+                eq(emailEntityLinks.tenantId, tenantId),
+                eq(emailEntityLinks.messageId, messageId),
+            ))
+
+        return (await Promise.all(links.map(async (link) => {
+            const entity = await loadEntity(tenantId, link.entityType, link.entityId)
+            return entity ? {
+                ...link,
+                entityName: entity.name,
+                entityTypeLabel: entity.typeLabel,
+            } : null
+        }))).filter(Boolean)
+    }
+
     const applyDownloadCorsHeaders = (req: any, reply: any) => {
         const origin = req.headers.origin
         if (
@@ -221,6 +276,8 @@ export default async function emailAsUserRoutes(server: FastifyInstance) {
                 html?: string
                 attachments?: any
                 account: string
+                sourceMessageId?: string
+                composeMode?: "reply" | "replyAll" | "forward"
             }
 
             // Fetch email credentials
@@ -248,6 +305,35 @@ export default async function emailAsUserRoutes(server: FastifyInstance) {
                 },
             })
 
+            const sourceMessage = body.sourceMessageId
+                ? await emailSync.getMessage(req.user.tenant_id, req.user.user_id, body.sourceMessageId)
+                : null
+
+            if (body.sourceMessageId && !sourceMessage) {
+                return reply.code(404).send({ error: "Ursprüngliche E-Mail nicht gefunden" })
+            }
+
+            const attachments = [...(Array.isArray(body.attachments) ? body.attachments : [])]
+
+            if (body.composeMode === "forward" && sourceMessage?.attachments?.length) {
+                for (const sourceAttachment of sourceMessage.attachments) {
+                    const attachment = await emailSync.getAttachmentContent(
+                        req.user.tenant_id,
+                        req.user.user_id,
+                        sourceAttachment.id,
+                    )
+                    if (!attachment) continue
+
+                    attachments.push({
+                        filename: attachment.filename,
+                        content: attachment.content,
+                        contentType: attachment.contentType,
+                        contentDisposition: "attachment",
+                    })
+                }
+            }
+
+            const isReply = body.composeMode === "reply" || body.composeMode === "replyAll"
             const message = {
                 from: accountData.email,
                 to: body.to,
@@ -256,7 +342,9 @@ export default async function emailAsUserRoutes(server: FastifyInstance) {
                 subject: body.subject,
                 html: body.html,
                 text: body.text,
-                attachments: body.attachments,
+                attachments,
+                inReplyTo: isReply ? sourceMessage?.messageId || undefined : undefined,
+                references: isReply && sourceMessage?.messageId ? [sourceMessage.messageId] : undefined,
             }
 
             const info = await transporter.sendMail(message)
@@ -381,13 +469,144 @@ export default async function emailAsUserRoutes(server: FastifyInstance) {
             const message = await emailSync.getMessage(req.user.tenant_id, req.user.user_id, id)
             if (!message) return reply.code(404).send({ error: "E-Mail nicht gefunden" })
 
-            return reply.send(message)
+            return reply.send({
+                ...message,
+                entityLinks: await listMessageEntityLinks(req.user.tenant_id, id),
+            })
         } catch (err: any) {
             req.log.error(err)
             return reply.code(500).send({ error: err.message || "E-Mail konnte nicht geladen werden" })
         }
     })
 
+    server.post("/email/messages/:id/entity-links", async (req, reply) => {
+        try {
+            if (!req.user?.tenant_id) {
+                return reply.code(400).send({ error: "No tenant selected" })
+            }
+
+            const { id } = req.params as { id: string }
+            const body = (req.body || {}) as { entityType?: string; entityId?: number | string }
+            const entityId = Number(body.entityId)
+
+            if (!body.entityType || !getEntityDefinition(body.entityType)) {
+                return reply.code(400).send({ error: "Nicht unterstützter Entitätstyp" })
+            }
+            if (!Number.isSafeInteger(entityId) || entityId <= 0) {
+                return reply.code(400).send({ error: "Ungültige Entitäts-ID" })
+            }
+
+            const message = await emailSync.getMessage(req.user.tenant_id, req.user.user_id, id)
+            if (!message) return reply.code(404).send({ error: "E-Mail nicht gefunden" })
+
+            const entity = await loadEntity(req.user.tenant_id, body.entityType, entityId)
+            if (!entity) return reply.code(404).send({ error: "Entität nicht gefunden" })
+
+            await server.db
+                .insert(emailEntityLinks)
+                .values({
+                    tenantId: req.user.tenant_id,
+                    messageId: id,
+                    entityType: body.entityType,
+                    entityId,
+                    linkedBy: req.user.user_id,
+                })
+                .onConflictDoNothing()
+
+            return reply.send({
+                success: true,
+                entityLinks: await listMessageEntityLinks(req.user.tenant_id, id),
+            })
+        } catch (err: any) {
+            req.log.error(err)
+            return reply.code(500).send({ error: err.message || "E-Mail konnte nicht verknüpft werden" })
+        }
+    })
+
+    server.delete("/email/messages/:id/entity-links/:entityType/:entityId", async (req, reply) => {
+        try {
+            if (!req.user?.tenant_id) {
+                return reply.code(400).send({ error: "No tenant selected" })
+            }
+
+            const { id, entityType, entityId: rawEntityId } = req.params as {
+                id: string
+                entityType: string
+                entityId: string
+            }
+            const entityId = Number(rawEntityId)
+
+            const message = await emailSync.getMessage(req.user.tenant_id, req.user.user_id, id)
+            if (!message) return reply.code(404).send({ error: "E-Mail nicht gefunden" })
+
+            await server.db
+                .delete(emailEntityLinks)
+                .where(and(
+                    eq(emailEntityLinks.tenantId, req.user.tenant_id),
+                    eq(emailEntityLinks.messageId, id),
+                    eq(emailEntityLinks.entityType, entityType),
+                    eq(emailEntityLinks.entityId, entityId),
+                ))
+
+            return reply.send({
+                success: true,
+                entityLinks: await listMessageEntityLinks(req.user.tenant_id, id),
+            })
+        } catch (err: any) {
+            req.log.error(err)
+            return reply.code(500).send({ error: err.message || "Verknüpfung konnte nicht entfernt werden" })
+        }
+    })
+
+    server.get("/email/entity-links/:entityType/:entityId", async (req, reply) => {
+        try {
+            if (!req.user?.tenant_id) {
+                return reply.code(400).send({ error: "No tenant selected" })
+            }
+
+            const { entityType, entityId: rawEntityId } = req.params as {
+                entityType: string
+                entityId: string
+            }
+            const entityId = Number(rawEntityId)
+
+            if (!getEntityDefinition(entityType)) {
+                return reply.code(400).send({ error: "Nicht unterstützter Entitätstyp" })
+            }
+            if (!Number.isSafeInteger(entityId) || entityId <= 0) {
+                return reply.code(400).send({ error: "Ungültige Entitäts-ID" })
+            }
+            if (!await loadEntity(req.user.tenant_id, entityType, entityId)) {
+                return reply.code(404).send({ error: "Entität nicht gefunden" })
+            }
+
+            const rows = await server.db
+                .select({
+                    message: emailMessages,
+                    linkId: emailEntityLinks.id,
+                    linkedAt: emailEntityLinks.createdAt,
+                })
+                .from(emailEntityLinks)
+                .innerJoin(emailMessages, eq(emailMessages.id, emailEntityLinks.messageId))
+                .where(and(
+                    eq(emailEntityLinks.tenantId, req.user.tenant_id),
+                    eq(emailEntityLinks.entityType, entityType),
+                    eq(emailEntityLinks.entityId, entityId),
+                ))
+                .orderBy(desc(emailMessages.receivedAt), desc(emailMessages.sentAt))
+
+            return reply.send(rows.map((row) => ({
+                ...row.message,
+                linkId: row.linkId,
+                linkedAt: row.linkedAt,
+                canOpen: row.message.userId === req.user.user_id,
+            })))
+        } catch (err: any) {
+            req.log.error(err)
+            return reply.code(500).send({ error: err.message || "Verknüpfte E-Mails konnten nicht geladen werden" })
+        }
+    })
+
     server.post("/email/messages/:id/read", async (req, reply) => {
         try {
             if (!req.user?.tenant_id) {
diff --git a/frontend/components/EntityShow.vue b/frontend/components/EntityShow.vue
index 9cca494..b8aa1d3 100644
--- a/frontend/components/EntityShow.vue
+++ b/frontend/components/EntityShow.vue
@@ -366,6 +366,11 @@ const invitePortalUser = async () => {
           v-else-if="tab.label === 'Zeiten'"
           :platform="platform"
       />
+      <EmailEntityMessages
+          v-else-if="tab.label === 'E-Mails'"
+          :entity-type="type"
+          :entity-id="props.item.id"
+      />
       <div v-else-if="tab.label === 'Wiki'" class="h-[600px] w-full overflow-hidden">
         <WikiEntityWidget
             :entity-type="type"
@@ -410,6 +415,11 @@ const invitePortalUser = async () => {
           @updateNeeded="emit('updateNeeded')"
           :platform="platform"
       />
+      <EmailEntityMessages
+          v-else-if="sub.label === 'E-Mails'"
+          :entity-type="type"
+          :entity-id="props.item.id"
+      />
       <!--<EntityShowSubPhases
           :item="props.item"
           :top-level-type="type"
diff --git a/frontend/components/email/EmailEntityLinks.vue b/frontend/components/email/EmailEntityLinks.vue
new file mode 100644
index 0000000..53c2f65
--- /dev/null
+++ b/frontend/components/email/EmailEntityLinks.vue
@@ -0,0 +1,169 @@
+<script setup lang="ts">
+type EntityLink = {
+  id: string
+  entityType: string
+  entityId: number
+  entityName: string
+  entityTypeLabel: string
+}
+
+const props = defineProps<{
+  messageId: string
+  entityLinks?: EntityLink[]
+}>()
+
+const emit = defineEmits<{
+  updated: [links: EntityLink[]]
+}>()
+
+const toast = useToast()
+const links = ref<EntityLink[]>([])
+const selectedEntityType = ref("customers")
+const selectedEntityId = ref<number | null>(null)
+const entityOptions = ref<Array<{ label: string; value: number }>>([])
+const loadingOptions = ref(false)
+const saving = ref(false)
+
+const entityTypes = [
+  { label: "Kunde", value: "customers" },
+  { label: "Lieferant", value: "vendors" },
+  { label: "Projekt", value: "projects" },
+  { label: "Objekt", value: "plants" },
+]
+
+watch(() => props.entityLinks, (value) => {
+  links.value = [...(value || [])]
+}, { immediate: true, deep: true })
+
+async function loadEntityOptions() {
+  loadingOptions.value = true
+  selectedEntityId.value = null
+
+  try {
+    const rows = await useEntities(selectedEntityType.value).select("*")
+    entityOptions.value = rows.map((row: any) => {
+      const number = row.customerNumber || row.vendorNumber || row.projectNumber
+      return {
+        label: number ? `${number} · ${row.name}` : row.name,
+        value: Number(row.id),
+      }
+    })
+  } catch (err: any) {
+    entityOptions.value = []
+    toast.add({
+      title: "Entitäten konnten nicht geladen werden",
+      description: err?.data?.error || err?.message,
+      color: "error",
+    })
+  } finally {
+    loadingOptions.value = false
+  }
+}
+
+async function addLink() {
+  if (!selectedEntityId.value) return
+
+  saving.value = true
+  try {
+    const response = await useNuxtApp().$api(`/api/email/messages/${props.messageId}/entity-links`, {
+      method: "POST",
+      body: {
+        entityType: selectedEntityType.value,
+        entityId: selectedEntityId.value,
+      },
+    })
+    links.value = response.entityLinks || []
+    emit("updated", links.value)
+    selectedEntityId.value = null
+    toast.add({ title: "E-Mail verknüpft", color: "success" })
+  } catch (err: any) {
+    toast.add({
+      title: "Verknüpfen fehlgeschlagen",
+      description: err?.data?.error || err?.message,
+      color: "error",
+    })
+  } finally {
+    saving.value = false
+  }
+}
+
+async function removeLink(link: EntityLink) {
+  saving.value = true
+  try {
+    const response = await useNuxtApp().$api(
+      `/api/email/messages/${props.messageId}/entity-links/${link.entityType}/${link.entityId}`,
+      { method: "DELETE" },
+    )
+    links.value = response.entityLinks || []
+    emit("updated", links.value)
+    toast.add({ title: "Verknüpfung entfernt", color: "success" })
+  } catch (err: any) {
+    toast.add({
+      title: "Entfernen fehlgeschlagen",
+      description: err?.data?.error || err?.message,
+      color: "error",
+    })
+  } finally {
+    saving.value = false
+  }
+}
+
+watch(selectedEntityType, loadEntityOptions, { immediate: true })
+</script>
+
+<template>
+  <div class="mt-4 rounded-lg border border-(--ui-border) bg-(--ui-bg-muted) p-3">
+    <div class="flex flex-wrap items-center gap-2">
+      <span class="text-sm font-medium">Verknüpft mit</span>
+      <UBadge
+        v-for="link in links"
+        :key="link.id"
+        color="primary"
+        variant="soft"
+        class="gap-1"
+      >
+        {{ link.entityTypeLabel }}: {{ link.entityName }}
+        <button
+          type="button"
+          class="ml-1 rounded hover:text-error"
+          :disabled="saving"
+          :aria-label="`Verknüpfung mit ${link.entityName} entfernen`"
+          @click="removeLink(link)"
+        >
+          <UIcon name="i-heroicons-x-mark" class="size-3.5" />
+        </button>
+      </UBadge>
+      <span v-if="!links.length" class="text-sm text-dimmed">Noch keine Zuordnung</span>
+    </div>
+
+    <div class="mt-3 flex flex-wrap items-center gap-2">
+      <USelectMenu
+        v-model="selectedEntityType"
+        :items="entityTypes"
+        value-key="value"
+        label-key="label"
+        size="sm"
+        class="w-36"
+      />
+      <USelectMenu
+        v-model="selectedEntityId"
+        :items="entityOptions"
+        value-key="value"
+        label-key="label"
+        size="sm"
+        class="min-w-64 flex-1"
+        placeholder="Entität auswählen"
+        :loading="loadingOptions"
+      />
+      <UButton
+        icon="i-heroicons-link"
+        size="sm"
+        :loading="saving"
+        :disabled="!selectedEntityId"
+        @click="addLink"
+      >
+        Verknüpfen
+      </UButton>
+    </div>
+  </div>
+</template>
diff --git a/frontend/components/email/EmailEntityMessages.vue b/frontend/components/email/EmailEntityMessages.vue
new file mode 100644
index 0000000..765c54e
--- /dev/null
+++ b/frontend/components/email/EmailEntityMessages.vue
@@ -0,0 +1,129 @@
+<script setup lang="ts">
+type EmailAddress = {
+  name?: string | null
+  address?: string | null
+}
+
+type LinkedMessage = {
+  id: string
+  accountId: string
+  mailboxPath: string
+  subject?: string | null
+  from?: EmailAddress[] | null
+  to?: EmailAddress[] | null
+  preview?: string | null
+  receivedAt?: string | null
+  sentAt?: string | null
+  linkedAt: string
+  hasAttachments: boolean
+  canOpen: boolean
+}
+
+const props = defineProps<{
+  entityType: string
+  entityId: string | number
+}>()
+
+const messages = ref<LinkedMessage[]>([])
+const loading = ref(true)
+const errorMessage = ref("")
+
+const formatAddress = (addresses?: EmailAddress[] | null) => {
+  const address = addresses?.[0]
+  if (!address) return "Unbekannt"
+  return address.name || address.address || "Unbekannt"
+}
+
+const formatDate = (value?: string | null) => {
+  if (!value) return ""
+  return new Intl.DateTimeFormat("de-DE", {
+    dateStyle: "medium",
+    timeStyle: "short",
+  }).format(new Date(value))
+}
+
+const openMessage = (message: LinkedMessage) => navigateTo({
+  path: "/email",
+  query: {
+    account: message.accountId,
+    mailbox: message.mailboxPath,
+    message: message.id,
+  },
+})
+
+async function loadMessages() {
+  loading.value = true
+  errorMessage.value = ""
+
+  try {
+    messages.value = await useNuxtApp().$api(
+      `/api/email/entity-links/${props.entityType}/${props.entityId}`,
+    )
+  } catch (err: any) {
+    errorMessage.value = err?.data?.error || err?.message || "Verknüpfte E-Mails konnten nicht geladen werden."
+  } finally {
+    loading.value = false
+  }
+}
+
+watch(() => [props.entityType, props.entityId], loadMessages, { immediate: true })
+</script>
+
+<template>
+  <div class="space-y-3">
+    <div v-if="loading" class="space-y-3">
+      <USkeleton v-for="index in 4" :key="index" class="h-28" />
+    </div>
+
+    <UAlert
+      v-else-if="errorMessage"
+      color="error"
+      icon="i-heroicons-exclamation-triangle"
+      title="E-Mails konnten nicht geladen werden"
+      :description="errorMessage"
+    />
+
+    <TableEmptyState
+      v-else-if="!messages.length"
+      label="Noch keine E-Mails mit dieser Entität verknüpft"
+    />
+
+    <article
+      v-for="message in messages"
+      v-else
+      :key="message.id"
+      class="rounded-lg border border-(--ui-border) bg-(--ui-bg) p-4"
+    >
+      <div class="flex items-start justify-between gap-4">
+        <div class="min-w-0">
+          <h3 class="truncate font-medium text-highlighted">
+            {{ message.subject || '(kein Betreff)' }}
+          </h3>
+          <p class="mt-1 text-sm text-dimmed">
+            Von {{ formatAddress(message.from) }} · {{ formatDate(message.receivedAt || message.sentAt) }}
+          </p>
+        </div>
+        <UButton
+          v-if="message.canOpen"
+          icon="i-heroicons-arrow-top-right-on-square"
+          color="neutral"
+          variant="soft"
+          size="sm"
+          @click="openMessage(message)"
+        >
+          Im Postfach öffnen
+        </UButton>
+      </div>
+      <p class="mt-3 line-clamp-2 text-sm text-muted">
+        {{ message.preview || 'Keine Vorschau verfügbar' }}
+      </p>
+      <div class="mt-3 flex items-center gap-3 text-xs text-dimmed">
+        <span>Verknüpft am {{ formatDate(message.linkedAt) }}</span>
+        <span v-if="message.hasAttachments" class="flex items-center gap-1">
+          <UIcon name="i-heroicons-paper-clip" class="size-3.5" />
+          Anhänge
+        </span>
+      </div>
+    </article>
+  </div>
+</template>
diff --git a/frontend/pages/email/index.vue b/frontend/pages/email/index.vue
index 6b4bead..568f2cd 100644
--- a/frontend/pages/email/index.vue
+++ b/frontend/pages/email/index.vue
@@ -52,9 +52,17 @@ type EmailMessage = {
     contentType?: string | null
     size?: number | null
   }>
+  entityLinks?: Array<{
+    id: string
+    entityType: string
+    entityId: number
+    entityName: string
+    entityTypeLabel: string
+  }>
 }
 
 const { $api } = useNuxtApp()
+const route = useRoute()
 const runtimeConfig = useRuntimeConfig()
 const toast = useToast()
 
@@ -74,6 +82,7 @@ const expandedMailboxPaths = ref<string[]>([])
 const syncedMailboxPaths = ref<string[]>([])
 const actionLoading = ref("")
 const moveTargetMailboxPath = ref("")
+let deepLinkApplied = false
 
 const selectedAccount = computed(() =>
     accounts.value.find((account) => account.id === selectedAccountId.value) || null
@@ -295,7 +304,10 @@ async function loadAccounts() {
   loadingAccounts.value = true
   try {
     accounts.value = await $api("/api/email/accounts")
-    selectedAccountId.value = accounts.value[0]?.id || ""
+    const requestedAccountId = String(route.query.account || "")
+    selectedAccountId.value = accounts.value.some((account) => account.id === requestedAccountId)
+      ? requestedAccountId
+      : accounts.value[0]?.id || ""
     if (selectedAccountId.value) {
       await loadMailboxes()
     }
@@ -316,7 +328,9 @@ async function loadMailboxes() {
     resetExpandedMailboxes()
     const inbox = mailboxes.value.find((mailbox) => mailbox.specialUse === "\\Inbox" || mailbox.path.toUpperCase() === "INBOX")
     const previousMailbox = mailboxes.value.find((mailbox) => mailbox.path === previousMailboxPath)
-    selectedMailboxPath.value = previousMailbox?.path || inbox?.path || mailboxes.value[0]?.path || "INBOX"
+    const requestedMailboxPath = String(route.query.mailbox || "")
+    const requestedMailbox = mailboxes.value.find((mailbox) => mailbox.path === requestedMailboxPath)
+    selectedMailboxPath.value = requestedMailbox?.path || previousMailbox?.path || inbox?.path || mailboxes.value[0]?.path || "INBOX"
     expandMailboxAncestors(selectedMailboxPath.value)
     await loadMessages()
   } finally {
@@ -340,7 +354,10 @@ async function loadMessages(options: { syncIfEmpty?: boolean } = {}) {
     }
 
     if (messages.value.length) {
-      await selectMessage(messages.value[0])
+      const requestedMessageId = deepLinkApplied ? "" : String(route.query.message || "")
+      const requestedMessage = messages.value.find((message) => message.id === requestedMessageId)
+      await selectMessage(requestedMessage || messages.value[0])
+      deepLinkApplied = true
     }
   } finally {
     loadingMessages.value = false
@@ -375,6 +392,22 @@ async function selectMessage(message: EmailMessage) {
   }
 }
 
+function updateSelectedMessageEntityLinks(entityLinks: NonNullable<EmailMessage["entityLinks"]>) {
+  if (!selectedMessage.value) return
+  selectedMessage.value = { ...selectedMessage.value, entityLinks }
+}
+
+function openComposer(mode: "reply" | "replyAll" | "forward") {
+  if (!selectedMessage.value) return
+  navigateTo({
+    path: "/email/new",
+    query: {
+      mode,
+      source: selectedMessage.value.id,
+    },
+  })
+}
+
 function removeMessageFromCurrentList(messageId: string) {
   const currentIndex = messages.value.findIndex((message) => message.id === messageId)
   messages.value = messages.value.filter((message) => message.id !== messageId)
@@ -800,16 +833,26 @@ onMounted(loadAccounts)
                     color="neutral"
                     variant="soft"
                     size="sm"
-                    @click="navigateTo(`/email/new?to=${encodeURIComponent(formatAddressList(selectedMessage.from))}&subject=${encodeURIComponent(`Re: ${selectedMessage.subject || ''}`)}`)"
+                    @click="openComposer('reply')"
                 >
                   Antworten
                 </UButton>
+                <UButton
+                    v-if="selectedMessage.cc?.length || (selectedMessage.to?.length || 0) > 1"
+                    icon="i-heroicons-users"
+                    color="neutral"
+                    variant="ghost"
+                    size="sm"
+                    @click="openComposer('replyAll')"
+                >
+                  Allen antworten
+                </UButton>
                 <UButton
                     icon="i-heroicons-arrow-uturn-right"
                     color="neutral"
                     variant="ghost"
                     size="sm"
-                    @click="navigateTo(`/email/new?subject=${encodeURIComponent(`Fw: ${selectedMessage.subject || ''}`)}`)"
+                    @click="openComposer('forward')"
                 >
                   Weiterleiten
                 </UButton>
@@ -831,6 +874,12 @@ onMounted(loadAccounts)
               </p>
             </div>
 
+            <EmailEntityLinks
+                :message-id="selectedMessage.id"
+                :entity-links="selectedMessage.entityLinks"
+                @updated="updateSelectedMessageEntityLinks"
+            />
+
             <div v-if="selectedMessage.attachments?.length" class="mt-4 flex flex-wrap gap-2">
               <button
                   v-for="attachment in selectedMessage.attachments"
diff --git a/frontend/pages/email/new.vue b/frontend/pages/email/new.vue
index bf5e4af..9651398 100644
--- a/frontend/pages/email/new.vue
+++ b/frontend/pages/email/new.vue
@@ -21,6 +21,55 @@ const preloadedContent = ref("")
 const loadedDocuments = ref([])
 const loaded = ref(false)
 const noAccountsPresent = ref(false)
+const sourceMessage = ref(null)
+const composeMode = computed(() => {
+  const mode = String(route.query.mode || "")
+  return ["reply", "replyAll", "forward"].includes(mode) ? mode : "new"
+})
+const pageTitle = computed(() => ({
+  reply: "Antworten",
+  replyAll: "Allen antworten",
+  forward: "E-Mail weiterleiten",
+}[composeMode.value] || "Neue E-Mail"))
+
+const escapeHtml = (value = "") => String(value)
+    .replace(/&/g, "&amp;")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;")
+    .replace(/'/g, "&#039;")
+
+const formatAddress = (address) => {
+  if (!address?.address) return ""
+  return address.name ? `"${String(address.name).replace(/"/g, "\\\"")}" <${address.address}>` : address.address
+}
+
+const formatAddressList = (addresses = []) => addresses.map(formatAddress).filter(Boolean).join(", ")
+
+const prefixedSubject = (prefix, subject = "") => {
+  const cleanSubject = String(subject || "")
+  return cleanSubject.toLowerCase().startsWith(prefix.toLowerCase()) ? cleanSubject : `${prefix} ${cleanSubject}`.trim()
+}
+
+const originalMessageBlock = (message, mode) => {
+  const sentAt = message.sentAt || message.receivedAt
+  const date = sentAt ? new Intl.DateTimeFormat("de-DE", {
+    dateStyle: "full",
+    timeStyle: "short",
+  }).format(new Date(sentAt)) : ""
+  const originalText = escapeHtml(message.body?.text || message.preview || "").replace(/\n/g, "<br>")
+
+  if (mode === "forward") {
+    return `<hr><p><strong>Weitergeleitete Nachricht</strong><br>`
+      + `Von: ${escapeHtml(formatAddressList(message.from))}<br>`
+      + `Datum: ${escapeHtml(date)}<br>`
+      + `Betreff: ${escapeHtml(message.subject || "(kein Betreff)")}<br>`
+      + `An: ${escapeHtml(formatAddressList(message.to))}</p><blockquote>${originalText}</blockquote>`
+  }
+
+  return `<hr><blockquote><p>Am ${escapeHtml(date)} schrieb ${escapeHtml(formatAddressList(message.from))}:</p>${originalText}</blockquote>`
+}
+
 const setupPage = async () => {
   //emailAccounts.value = await useEntities("emailAccounts").select()
 
@@ -31,7 +80,41 @@ const setupPage = async () => {
   } else {
     emailData.value.account = emailAccounts.value[0].id
 
-    preloadedContent.value = `<p></p><p></p><p></p>${auth.profile.email_signature || ""}`
+    let initialContent = `<p></p><p></p><p></p>${auth.profile.email_signature || ""}`
+
+    if (route.query.source && composeMode.value !== "new") {
+      sourceMessage.value = await useNuxtApp().$api(`/api/email/messages/${route.query.source}`)
+      const sourceAccount = emailAccounts.value.find(account => account.id === sourceMessage.value.accountId)
+      if (sourceAccount) emailData.value.account = sourceAccount.id
+
+      if (composeMode.value === "forward") {
+        emailData.value.subject = prefixedSubject("Fw:", sourceMessage.value.subject)
+      } else {
+        const ownAddress = String(sourceAccount?.email || "").toLowerCase()
+        const replyRecipients = sourceMessage.value.replyTo?.length
+            ? sourceMessage.value.replyTo
+            : sourceMessage.value.from || []
+
+        if (composeMode.value === "replyAll") {
+          const allRecipients = [
+            ...replyRecipients,
+            ...(sourceMessage.value.to || []),
+            ...(sourceMessage.value.cc || []),
+          ].filter(address => address?.address && address.address.toLowerCase() !== ownAddress)
+          const uniqueRecipients = Array.from(new Map(
+              allRecipients.map(address => [address.address.toLowerCase(), address])
+          ).values())
+          emailData.value.to = formatAddressList(uniqueRecipients)
+        } else {
+          emailData.value.to = formatAddressList(replyRecipients)
+        }
+        emailData.value.subject = prefixedSubject("Re:", sourceMessage.value.subject)
+      }
+
+      initialContent += originalMessageBlock(sourceMessage.value, composeMode.value)
+    }
+
+    preloadedContent.value = initialContent
 
     //Check Query
     if(route.query.to) emailData.value.to = route.query.to
@@ -120,7 +203,9 @@ const sendEmail = async () => {
 
   let body  = {
     ...emailData.value,
-    attachments: []
+    attachments: [],
+    sourceMessageId: sourceMessage.value?.id,
+    composeMode: composeMode.value === "new" ? undefined : composeMode.value,
   }
 
 
@@ -151,26 +236,28 @@ const sendEmail = async () => {
     })
   }
 
-  console.log(body)
+  try {
+    const res = await useNuxtApp().$api("/api/email/send",{
+      method: "POST",
+      body: body,
+    })
 
-  const res = await useNuxtApp().$api("/api/email/send",{
-    method: "POST",
-    body: body,
-  })
-
-  console.log(res)
-
-
-  if(!res.success) {
-    toast.add({title: "Fehler beim Absenden der E-Mail", color: "error"})
-
-  } else {
-    navigateTo("/")
-    toast.add({title: "E-Mail zum Senden eingereiht"})
+    if(!res.success) {
+      toast.add({title: "Fehler beim Absenden der E-Mail", color: "error"})
+    } else {
+      await navigateTo("/email")
+      toast.add({title: "E-Mail gesendet", color: "success"})
+    }
+  } catch (err) {
+    toast.add({
+      title: "Fehler beim Absenden der E-Mail",
+      description: err?.data?.error || err?.message,
+      color: "error",
+    })
+  } finally {
+    loaded.value = true
   }
 
-  loaded.value = true
-
 }
 
 
@@ -192,7 +279,7 @@ const sendEmail = async () => {
 
     <div v-else>
       <UDashboardNavbar
-          title="Neue E-Mail"
+          :title="pageTitle"
       >
         <template #right>
           <UButton
@@ -280,6 +367,12 @@ const sendEmail = async () => {
             >
               <span v-if="doc.createddocument">Dokument - {{doc.createddocument.documentNumber}}</span>
             </li>
+            <li
+                v-if="composeMode === 'forward' && sourceMessage?.attachments?.length"
+                class="list-disc"
+            >
+              {{ sourceMessage.attachments.length }} Originalanhang/Originalanhänge werden übernommen
+            </li>
           </ul>
 
         </div>
diff --git a/frontend/stores/data.js b/frontend/stores/data.js
index f71993d..7dcde80 100644
--- a/frontend/stores/data.js
+++ b/frontend/stores/data.js
@@ -494,7 +494,7 @@ export const useDataStore = defineStore('data', () => {
                     inputColumn: "Allgemeines"
                 },*/
             ],
-            showTabs: [{label: 'Informationen'},{label: 'Ansprechpartner'},{label: 'Dateien'},{label: 'Ausgangsbelege'},{label: 'Projekte'},{label: 'Objekte'},{label: 'Termine'},{label: 'Verträge'},{label: 'Ausgehende SEPA-Mandate', key: 'outgoingsepamandates', type: 'outgoingsepamandates'},{label: 'Kundeninventar', key: 'customerinventoryitems'},{label: 'Kundenlagerplätze', key: 'customerspaces'},{label: 'Wiki'}]
+            showTabs: [{label: 'Informationen'},{label: 'Ansprechpartner'},{label: 'E-Mails'},{label: 'Dateien'},{label: 'Ausgangsbelege'},{label: 'Projekte'},{label: 'Objekte'},{label: 'Termine'},{label: 'Verträge'},{label: 'Ausgehende SEPA-Mandate', key: 'outgoingsepamandates', type: 'outgoingsepamandates'},{label: 'Kundeninventar', key: 'customerinventoryitems'},{label: 'Kundenlagerplätze', key: 'customerspaces'},{label: 'Wiki'}]
         },
         members: {
             isArchivable: true,
@@ -1463,6 +1463,8 @@ export const useDataStore = defineStore('data', () => {
                 label: "Projekte"
             },{
                 label: "Aufgaben"
+            },{
+                label: "E-Mails"
             },{
                 label: "Dateien"
             },{
@@ -1741,6 +1743,8 @@ export const useDataStore = defineStore('data', () => {
                 },{
                     key: "tasks",
                     label: "Aufgaben"
+                },{
+                    label: "E-Mails"
                 },{
                     key: "files",
                     label: "Dateien"
@@ -2024,6 +2028,8 @@ export const useDataStore = defineStore('data', () => {
                     label: 'Informationen',
                 },{
                     label: 'Ansprechpartner',
+                }, {
+                    label: 'E-Mails',
                 }, {
                     label: 'Dateien',
                 }, {