diff --git a/backend/src/routes/emailAsUser.ts b/backend/src/routes/emailAsUser.ts
index ff68692..017c193 100644
--- a/backend/src/routes/emailAsUser.ts
+++ b/backend/src/routes/emailAsUser.ts
@@ -23,27 +23,62 @@ export default async function emailAsUserRoutes(server: FastifyInstance) {
 
     const encryptedValue = (value: unknown) => value ? decrypt(value as any) : null
 
-    const accountResponse = (row: any) => ({
-        id: row.id,
-        createdAt: row.createdAt,
-        updatedAt: row.updatedAt,
-        userId: row.userId,
-        tenantId: row.tenantId,
-        type: row.type,
-        email: encryptedValue(row.emailEncrypted),
-        smtpHost: encryptedValue(row.smtpHostEncrypted),
-        smtpPort: row.smtpPort ? Number(row.smtpPort) : null,
-        smtpSsl: row.smtpSsl,
-        imapHost: encryptedValue(row.imapHostEncrypted),
-        imapPort: row.imapPort ? Number(row.imapPort) : null,
-        imapSsl: row.imapSsl,
-        hasPassword: Boolean(row.passwordEncrypted),
-    })
+    const accountResponse = (row: any) => {
+        const invalidEncryptedFields: string[] = []
+        const safeEncryptedValue = (value: unknown, field: string) => {
+            if (!value) return null
+            try {
+                return encryptedValue(value)
+            } catch {
+                invalidEncryptedFields.push(field)
+                return null
+            }
+        }
 
-    const accountCredentials = (row: any) => ({
-        ...accountResponse(row),
-        password: encryptedValue(row.passwordEncrypted),
-    })
+        const email = safeEncryptedValue(row.emailEncrypted, "email")
+        const smtpHost = safeEncryptedValue(row.smtpHostEncrypted, "smtpHost")
+        const imapHost = safeEncryptedValue(row.imapHostEncrypted, "imapHost")
+        safeEncryptedValue(row.passwordEncrypted, "password")
+
+        if (invalidEncryptedFields.length) {
+            server.log.warn({
+                accountId: row.id,
+                invalidEncryptedFields,
+            }, "E-Mail-Kontodaten können mit dem aktuellen ENCRYPTION_KEY nicht entschlüsselt werden")
+        }
+
+        return {
+            id: row.id,
+            createdAt: row.createdAt,
+            updatedAt: row.updatedAt,
+            userId: row.userId,
+            tenantId: row.tenantId,
+            type: row.type,
+            email,
+            displayName: email || `Mailkonto ${String(row.id).slice(0, 8)} muss repariert werden`,
+            smtpHost,
+            smtpPort: row.smtpPort ? Number(row.smtpPort) : null,
+            smtpSsl: row.smtpSsl,
+            imapHost,
+            imapPort: row.imapPort ? Number(row.imapPort) : null,
+            imapSsl: row.imapSsl,
+            hasPassword: Boolean(row.passwordEncrypted),
+            credentialsReadable: invalidEncryptedFields.length === 0,
+            invalidEncryptedFields,
+        }
+    }
+
+    const accountCredentials = (row: any) => {
+        const account = accountResponse(row)
+        if (!account.credentialsReadable) {
+            throw new Error("Die verschlüsselten Kontodaten sind nicht lesbar. Bitte das E-Mail-Konto in den Einstellungen vollständig neu speichern.")
+        }
+
+        return {
+            ...account,
+            password: encryptedValue(row.passwordEncrypted),
+        }
+    }
 
     const bodyValue = (body: any, camelKey: string, snakeKey: string) => body[camelKey] ?? body[snakeKey]
 
diff --git a/frontend/pages/email/index.vue b/frontend/pages/email/index.vue
index 568f2cd..cca6da7 100644
--- a/frontend/pages/email/index.vue
+++ b/frontend/pages/email/index.vue
@@ -5,6 +5,8 @@ import { de as deLocale } from "date-fns/locale"
 type EmailAccount = {
   id: string
   email: string
+  displayName?: string
+  credentialsReadable?: boolean
   imapHost?: string | null
   hasPassword?: boolean
 }
@@ -657,7 +659,7 @@ onMounted(loadAccounts)
               v-else-if="accounts.length"
               v-model="selectedAccountId"
               :items="accounts"
-              label-key="email"
+              label-key="displayName"
               value-key="id"
               class="w-full"
           />
diff --git a/frontend/pages/email/new.vue b/frontend/pages/email/new.vue
index 9651398..9e66b48 100644
--- a/frontend/pages/email/new.vue
+++ b/frontend/pages/email/new.vue
@@ -302,7 +302,7 @@ const sendEmail = async () => {
           >
             <USelectMenu
                 :items="emailAccounts"
-                label-key="email"
+                label-key="displayName"
                 value-key="id"
                 v-model="emailData.account"
             />
diff --git a/frontend/pages/settings/emailaccounts/[mode]/[[id]].vue b/frontend/pages/settings/emailaccounts/[mode]/[[id]].vue
index 3039448..e623f33 100644
--- a/frontend/pages/settings/emailaccounts/[mode]/[[id]].vue
+++ b/frontend/pages/settings/emailaccounts/[mode]/[[id]].vue
@@ -5,6 +5,7 @@ const toast = useToast()
 const mode = route.params.mode
 const isCreate = computed(() => mode === "create")
 const loading = ref(false)
+const credentialsReadable = ref(true)
 
 const itemInfo = ref({
   email: "",
@@ -20,6 +21,7 @@ const itemInfo = ref({
 const setup = async () => {
   if(!isCreate.value) {
     const account = await useNuxtApp().$api(`/api/email/accounts/${route.params.id}`)
+    credentialsReadable.value = account.credentialsReadable !== false
     itemInfo.value = {
       ...itemInfo.value,
       ...account,
@@ -36,6 +38,13 @@ const payload = () => ({
   password: itemInfo.value.password || undefined,
 })
 
+const canSave = computed(() => Boolean(
+    itemInfo.value.email
+    && itemInfo.value.imapHost
+    && itemInfo.value.smtpHost
+    && (isCreate.value || credentialsReadable.value || itemInfo.value.password)
+))
+
 const createAccount = async () => {
   loading.value = true
   const res = await useNuxtApp().$api(`/api/email/accounts`, {
@@ -123,7 +132,7 @@ const syncAccount = async () => {
         v-if="!isCreate"
         icon="i-heroicons-check"
         :loading="loading"
-        :disabled="!itemInfo.email || !itemInfo.imapHost || !itemInfo.smtpHost"
+        :disabled="!canSave"
         @click="saveAccount"
       >
         Speichern
@@ -132,6 +141,16 @@ const syncAccount = async () => {
   </UDashboardNavbar>
 
   <div class="mx-auto max-w-4xl p-4">
+    <UAlert
+        v-if="!isCreate && !credentialsReadable"
+        class="mb-4"
+        color="error"
+        variant="soft"
+        icon="i-heroicons-exclamation-triangle"
+        title="Zugangsdaten müssen repariert werden"
+        description="Die Daten wurden mit einem anderen oder nicht mehr verfügbaren Verschlüsselungsschlüssel gespeichert. Trage E-Mail-Adresse, Passwort, IMAP-Host und SMTP-Host vollständig neu ein und speichere das Konto."
+    />
+
     <UAlert
         v-if="!isCreate"
         class="mb-4"
@@ -139,7 +158,7 @@ const syncAccount = async () => {
         variant="soft"
         icon="i-heroicons-lock-closed"
         title="Passwort bleibt geschützt"
-        description="Das gespeicherte Passwort wird nicht angezeigt. Trage nur dann ein neues Passwort ein, wenn du es ändern möchtest."
+        :description="credentialsReadable ? 'Das gespeicherte Passwort wird nicht angezeigt. Trage nur dann ein neues Passwort ein, wenn du es ändern möchtest.' : 'Das bisherige Passwort kann nicht entschlüsselt werden und muss neu eingetragen werden.'"
     />
 
     <UForm class="grid gap-6">
@@ -158,11 +177,11 @@ const syncAccount = async () => {
             />
           </UFormField>
 
-          <UFormField :label="isCreate ? 'Passwort' : 'Neues Passwort'">
+          <UFormField :label="isCreate || !credentialsReadable ? 'Passwort' : 'Neues Passwort'">
             <UInput
                 v-model="itemInfo.password"
                 type="password"
-                :placeholder="isCreate ? '' : 'Unverändert lassen'"
+                :placeholder="isCreate || !credentialsReadable ? '' : 'Unverändert lassen'"
             />
           </UFormField>
         </div>
diff --git a/frontend/pages/settings/emailaccounts/index.vue b/frontend/pages/settings/emailaccounts/index.vue
index ab5aeb4..6f824b7 100644
--- a/frontend/pages/settings/emailaccounts/index.vue
+++ b/frontend/pages/settings/emailaccounts/index.vue
@@ -73,7 +73,7 @@ setupPage()
         <div class="flex items-center gap-2">
           <UIcon name="i-heroicons-envelope" class="size-5 text-primary" />
           <p class="truncate font-medium">
-            {{ account.email }}
+            {{ account.displayName || account.email }}
           </p>
           <UBadge
               size="xs"
@@ -88,6 +88,9 @@ setupPage()
           <span>SMTP: {{ account.smtpHost || "nicht gesetzt" }}:{{ account.smtpPort || "-" }}</span>
           <span>{{ account.hasPassword ? "Passwort hinterlegt" : "Passwort fehlt" }}</span>
         </div>
+        <p v-if="account.credentialsReadable === false" class="mt-2 text-sm text-error">
+          Die verschlüsselten Zugangsdaten sind nicht lesbar. Öffne das Konto und trage alle Zugangsdaten neu ein.
+        </p>
       </div>
 
       <div class="flex shrink-0 items-center gap-2">
@@ -96,6 +99,7 @@ setupPage()
             color="neutral"
             variant="soft"
             :loading="syncingAccount === account.id"
+            :disabled="account.credentialsReadable === false"
             @click.stop="syncAccount(account)"
         >
           Synchronisieren