diff --git a/partials/landingpage/accountsetup/settings.php b/partials/landingpage/accountsetup/settings.php
index c920885..e0c8486 100755
--- a/partials/landingpage/accountsetup/settings.php
+++ b/partials/landingpage/accountsetup/settings.php
@@ -59,6 +59,9 @@ require dirname(__DIR__) . '/../structure/layout_start.php';
         <label class="block text-sm text-slate-600">Bezeichnung
           <input type="text" name="label" class="input mt-1" placeholder="Profil-Name">
         </label>
+        <label class="inline-flex items-center gap-2 text-sm text-slate-600">
+          <input type="checkbox" name="is_default" value="1"> Als Standard-Testprofil verwenden
+        </label>
         <div class="grid md:grid-cols-2 gap-3">
           <label class="block text-sm text-slate-600">SMTP-Server
             <input type="text" name="smtp_host" class="input mt-1" placeholder="smtp.example.com">
diff --git a/public/assets/js/ui-editor.js b/public/assets/js/ui-editor.js
index c46c478..ae87ca8 100755
--- a/public/assets/js/ui-editor.js
+++ b/public/assets/js/ui-editor.js
@@ -949,13 +949,15 @@ export function initEditor() {
     let html = '<option value="">Standard (System)</option>';
     smtpProfileOptions.forEach(opt => {
       const label = opt.label || opt.smtp_host || 'Profil';
-      html += `<option value="${opt.id}">${escapeHtml(label)}</option>`;
+      const suffix = opt.is_default ? ' (Standard)' : '';
+      html += `<option value="${opt.id}">${escapeHtml(label + suffix)}</option>`;
     });
     sendSmtpProfile.innerHTML = html;
     if (previous && smtpProfileOptions.some(opt => String(opt.id) === previous)) {
       sendSmtpProfile.value = previous;
     } else {
-      sendSmtpProfile.value = '';
+      const def = smtpProfileOptions.find(opt => opt.is_default);
+      sendSmtpProfile.value = def ? String(def.id) : '';
     }
     if (sendSmtpProfileHint) {
       sendSmtpProfileHint.classList.toggle('hidden', smtpProfileOptions.length > 0);
diff --git a/public/assets/js/ui-user.js b/public/assets/js/ui-user.js
index 498cb02..445a0f6 100755
--- a/public/assets/js/ui-user.js
+++ b/public/assets/js/ui-user.js
@@ -921,7 +921,7 @@ function renderSmtpProfileList() {
     const sender = profile.from_email || '—';
     return `
     <tr>
-      <td>${escapeHtml(label)}</td>
+      <td>${escapeHtml(label)}${profile.is_default ? ' <span class="text-xs text-slate-500">(Standard)</span>' : ''}</td>
       <td>${escapeHtml(host)}</td>
       <td>${escapeHtml(user)}</td>
       <td>${escapeHtml(sender)}</td>
@@ -930,6 +930,7 @@ function renderSmtpProfileList() {
         <button class="btn" data-smtp-action="edit" data-smtp-id="${profile.id}">Bearbeiten</button>
         <button class="btn" data-smtp-action="copy" data-smtp-id="${profile.id}">Kopieren</button>
         <button class="btn btn-danger" data-smtp-action="delete" data-smtp-id="${profile.id}">Löschen</button>
+        ${profile.is_default ? '' : `<button class="btn" data-smtp-action="set-default" data-smtp-id="${profile.id}">Standard</button>`}
       </td>
     </tr>`;
   }).join('');
@@ -946,6 +947,8 @@ function handleSmtpProfileTableClick(ev) {
     openSmtpProfileForm(profile);
   } else if (action === 'test') {
     runSmtpProfileTest(profile.id);
+  } else if (action === 'set-default') {
+    setDefaultSmtpProfile(profile.id);
   } else if (action === 'copy') {
     if (confirm(`Versandprofil "${profile.label || profile.smtp_host}" kopieren?`)) {
       copySmtpProfile(id);
@@ -971,6 +974,7 @@ function openSmtpProfileForm(profile = null) {
   smtpProfileForm.from_email.value = profile?.from_email || '';
   smtpProfileForm.from_name.value = profile?.from_name || '';
   smtpProfileForm.reply_to.value = profile?.reply_to || '';
+  smtpProfileForm.is_default.checked = !!profile?.is_default;
   if (smtpProfileForm.smtp_pass_clear) smtpProfileForm.smtp_pass_clear.checked = false;
 }
 
@@ -996,6 +1000,7 @@ async function submitSmtpProfileForm(ev) {
     from_name: smtpProfileForm.from_name.value.trim(),
     reply_to: smtpProfileForm.reply_to.value.trim(),
     smtp_pass_clear: smtpProfileForm.smtp_pass_clear?.checked ? 1 : 0,
+    is_default: smtpProfileForm.is_default?.checked ? 1 : 0,
   };
   if (!payload.smtp_host) {
     toast('Bitte einen SMTP-Server angeben', false);
@@ -1046,6 +1051,17 @@ async function runSmtpProfileTest(profileId) {
   }
 }
 
+async function setDefaultSmtpProfile(profileId) {
+  try {
+    const res = await apiAction('account.smtp_profiles.save', { method: 'POST', data: { profile_id: profileId, is_default: 1 } });
+    if (!res?.ok) throw new Error(res?.error || 'Standard konnte nicht gesetzt werden');
+    await loadSmtpProfiles();
+    toast('Standard-Testprofil gesetzt', true);
+  } catch (err) {
+    toast(err.message || 'Standard konnte nicht gesetzt werden', false);
+  }
+}
+
 function escapeHtml(str) {
   return String(str || '')
     .replace(/&/g, '&amp;')
diff --git a/schema.sql b/schema.sql
index af0e902..6d3681c 100755
--- a/schema.sql
+++ b/schema.sql
@@ -225,6 +225,7 @@ CREATE TABLE IF NOT EXISTS `emailtemplate_smtp_profiles` (
   `from_email` varchar(255) DEFAULT NULL,
   `from_name` varchar(255) DEFAULT NULL,
   `reply_to` varchar(255) DEFAULT NULL,
+  `is_default` tinyint(1) DEFAULT 0,
   `created_at` timestamp NOT NULL DEFAULT current_timestamp(),
   `updated_at` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(),
   PRIMARY KEY (`id`),
diff --git a/src/ApiKernel.php b/src/ApiKernel.php
index 89cd1f8..6951965 100755
--- a/src/ApiKernel.php
+++ b/src/ApiKernel.php
@@ -2248,6 +2248,9 @@ class ApiKernel
         }
         $senderId = (int)$this->val($this->in, ['sender_id'], 0);
         $smtpProfileId = (int)$this->val($this->in, ['smtp_profile_id'], 0);
+        if ($smtpProfileId <= 0 && $customerId > 0) {
+            $smtpProfileId = $this->getDefaultSmtpProfileId($customerId);
+        }
 
         $row = null;
         $html = '';
@@ -4369,6 +4372,32 @@ class ApiKernel
         $fromName = trim((string)($this->in['from_name'] ?? ''));
         $replyTo = trim((string)($this->in['reply_to'] ?? ''));
         $passClear = !empty($this->in['smtp_pass_clear']);
+        $isDefault = !empty($this->in['is_default']);
+
+        $defaultOnly = $profileId > 0
+            && $isDefault
+            && $label === ''
+            && $host === ''
+            && $port === 0
+            && $userName === ''
+            && $pass === ''
+            && $secure === ''
+            && $fromEmail === ''
+            && $fromName === ''
+            && $replyTo === ''
+            && !$passClear;
+
+        if ($defaultOnly) {
+            $this->ensureSmtpProfilesTableExists();
+            $table = $this->smtpProfilesTable();
+            $stmt = $this->pdo->prepare("UPDATE `$table` SET `is_default` = 0 WHERE `customer_id` = :cid AND `id` != :id");
+            $stmt->execute([':cid' => $customerId, ':id' => $profileId]);
+            $stmt = $this->pdo->prepare("UPDATE `$table` SET `is_default` = 1 WHERE `id` = :id AND `customer_id` = :cid");
+            $stmt->execute([':id' => $profileId, ':cid' => $customerId]);
+            $profile = $this->fetchSmtpProfileRow($customerId, $profileId);
+            $this->respond(['ok' => true, 'profile' => $profile]);
+            return;
+        }
 
         if ($label === '') $label = $fromEmail ?: $host;
         if ($host === '') $this->fail('SMTP-Host erforderlich', null, 422);
@@ -4397,6 +4426,7 @@ class ApiKernel
                 'from_email' => $fromEmail ?: null,
                 'from_name' => $fromName ?: null,
                 'reply_to' => $replyTo ?: null,
+                'is_default' => $isDefault ? 1 : 0,
             ];
             if ($passClear) {
                 $fields['smtp_pass'] = null;
@@ -4415,7 +4445,7 @@ class ApiKernel
             $stmt->execute($params);
             if ($stmt->rowCount() === 0) $this->fail('Versandprofil nicht gefunden', null, 404);
         } else {
-            $stmt = $this->pdo->prepare("INSERT INTO `$table` (`customer_id`,`label`,`smtp_host`,`smtp_port`,`smtp_user`,`smtp_pass`,`smtp_secure`,`from_email`,`from_name`,`reply_to`,`created_at`,`updated_at`) VALUES (:cid,:label,:host,:port,:user,:pass,:secure,:fmail,:fname,:reply,NOW(),NOW())");
+            $stmt = $this->pdo->prepare("INSERT INTO `$table` (`customer_id`,`label`,`smtp_host`,`smtp_port`,`smtp_user`,`smtp_pass`,`smtp_secure`,`from_email`,`from_name`,`reply_to`,`is_default`,`created_at`,`updated_at`) VALUES (:cid,:label,:host,:port,:user,:pass,:secure,:fmail,:fname,:reply,:is_default,NOW(),NOW())");
             $stmt->execute([
                 ':cid' => $customerId,
                 ':label' => $label,
@@ -4427,8 +4457,20 @@ class ApiKernel
                 ':fmail' => $fromEmail ?: null,
                 ':fname' => $fromName ?: null,
                 ':reply' => $replyTo ?: null,
+                ':is_default' => $isDefault ? 1 : 0,
             ]);
             $profileId = (int)$this->pdo->lastInsertId();
+            if ($isDefault) {
+                $stmt = $this->pdo->prepare("UPDATE `$table` SET `is_default` = 0 WHERE `customer_id` = :cid AND `id` != :id");
+                $stmt->execute([':cid' => $customerId, ':id' => $profileId]);
+                $stmt = $this->pdo->prepare("UPDATE `$table` SET `is_default` = 1 WHERE `id` = :id AND `customer_id` = :cid");
+                $stmt->execute([':id' => $profileId, ':cid' => $customerId]);
+            }
+        }
+
+        if ($profileId > 0 && $isDefault) {
+            $stmt = $this->pdo->prepare("UPDATE `$table` SET `is_default` = 0 WHERE `customer_id` = :cid AND `id` != :id");
+            $stmt->execute([':cid' => $customerId, ':id' => $profileId]);
         }
 
         $profile = $this->fetchSmtpProfileRow($customerId, $profileId);
@@ -5502,6 +5544,7 @@ SQL;
     {
         $table = $this->smtpProfilesTable();
         if ($this->tableExists($table)) {
+            $this->ensureSmtpProfilesColumns($table);
             return;
         }
         try {
@@ -5518,6 +5561,7 @@ CREATE TABLE IF NOT EXISTS `$table` (
   `from_email` varchar(255) DEFAULT NULL,
   `from_name` varchar(255) DEFAULT NULL,
   `reply_to` varchar(255) DEFAULT NULL,
+  `is_default` tinyint(1) DEFAULT 0,
   `created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
   `updated_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
   PRIMARY KEY (`id`),
@@ -5533,6 +5577,27 @@ SQL;
         }
     }
 
+    private function ensureSmtpProfilesColumns(string $table): void
+    {
+        try {
+            $columns = $this->tableColumns($table);
+        } catch (Throwable $e) {
+            $this->fail('SMTP-Profil-Tabelle konnte nicht gelesen werden', $e->getMessage(), 500);
+            return;
+        }
+        $missing = [];
+        if (!in_array('is_default', $columns, true)) {
+            $missing[] = 'ADD COLUMN `is_default` tinyint(1) DEFAULT 0';
+        }
+        if (!$missing) return;
+        try {
+            $sql = 'ALTER TABLE `' . $table . '` ' . implode(', ', $missing);
+            $this->pdo->exec($sql);
+        } catch (Throwable $e) {
+            $this->fail('SMTP-Profil-Tabelle konnte nicht aktualisiert werden', $e->getMessage(), 500);
+        }
+    }
+
     private function fetchSenderRow(int $customerId, int $senderId): array
     {
         if ($customerId <= 0 || $senderId <= 0) {
@@ -5599,12 +5664,23 @@ SQL;
             'from_email' => $row['from_email'] ?? '',
             'from_name' => $row['from_name'] ?? '',
             'reply_to' => $row['reply_to'] ?? '',
+            'is_default' => !empty($row['is_default']) ? 1 : 0,
             'smtp_pass_set' => $pass !== '',
             'created_at' => $row['created_at'] ?? null,
             'updated_at' => $row['updated_at'] ?? null,
         ];
     }
 
+    private function getDefaultSmtpProfileId(int $customerId): int
+    {
+        if ($customerId <= 0) return 0;
+        $this->ensureSmtpProfilesTableExists();
+        $table = $this->smtpProfilesTable();
+        $stmt = $this->pdo->prepare("SELECT `id` FROM `$table` WHERE `customer_id` = :cid AND `is_default` = 1 ORDER BY `id` ASC LIMIT 1");
+        $stmt->execute([':cid' => $customerId]);
+        return (int)($stmt->fetchColumn() ?: 0);
+    }
+
     private function formatUserOutput(array $row): array
     {
         return [