fix: add separate sender/recipient email fields for SMTP notification channel

The email (SMTP) form previously used the `username` field as both SMTP
auth credential and the from/to address. This breaks services like
Postmark that use API tokens as SMTP credentials.

Changes:
- Added "Sender Email (From)" (optional) and "Recipient Email (To)"
  (required) fields to the email channel configuration
- Renamed "Username / Email" to "SMTP Username" for clarity
- Updated `buildAppriseUrl` to build `mailto://user:pass@host/?to=...&from=...`
  so recipient and sender are explicit query parameters
- Updated tests to match new field labels and added two new email URL tests

Agent-Logs-Url: https://github.com/christianlouis/InboxConverge/sessions/5be072bb-0824-436b-983b-1a6bb6df2699

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/src/components/NotificationWizard.test.tsx

@@ -79,10 +79,12 @@ describe('NotificationWizard', () => {
 
     it('should show Email fields', () => {
       goToStep2('Email');
-      expect(screen.getByText('Username / Email')).toBeInTheDocument();
+      expect(screen.getByText('SMTP Username')).toBeInTheDocument();
       expect(screen.getByText('SMTP Password')).toBeInTheDocument();
       expect(screen.getByText('SMTP Host')).toBeInTheDocument();
       expect(screen.getByText('SMTP Port')).toBeInTheDocument();
+      expect(screen.getByText('Sender Email (From)')).toBeInTheDocument();
+      expect(screen.getByText('Recipient Email (To)')).toBeInTheDocument();
     });
 
     it('should show Webhook fields', () => {
@@ -294,6 +296,72 @@ describe('NotificationWizard', () => {
       });
       expect(url).toBe('tgram://mybot/mychat/');
     });
+
+    it('should build correct Email URL with recipient only', () => {
+      render(<NotificationWizard onComplete={mockOnComplete} onCancel={mockOnCancel} />);
+      fireEvent.click(screen.getByText('Email'));
+
+      fireEvent.change(screen.getByPlaceholderText('user@example.com or API key'), {
+        target: { value: 'apikey' },
+      });
+      fireEvent.change(document.querySelector('input[type="password"]')!, {
+        target: { value: 'secret' },
+      });
+      fireEvent.change(screen.getByPlaceholderText('smtp.example.com'), {
+        target: { value: 'smtp.postmarkapp.com' },
+      });
+      fireEvent.change(screen.getByPlaceholderText('587'), {
+        target: { value: '587' },
+      });
+      // sender left blank (optional)
+      fireEvent.change(screen.getByPlaceholderText('you@example.com'), {
+        target: { value: 'me@example.com' },
+      });
+
+      fireEvent.click(screen.getByText('Next').closest('button')!);
+      fireEvent.change(screen.getByPlaceholderText('e.g. My Telegram Alert'), {
+        target: { value: 'Postmark' },
+      });
+      fireEvent.click(screen.getByText('Save Channel').closest('button')!);
+
+      const url = mockOnComplete.mock.calls[0][0].apprise_url as string;
+      expect(url).toContain('mailto://apikey:secret@smtp.postmarkapp.com:587/');
+      expect(url).toContain('to=me%40example.com');
+      expect(url).not.toContain('from=');
+    });
+
+    it('should build correct Email URL with both sender and recipient', () => {
+      render(<NotificationWizard onComplete={mockOnComplete} onCancel={mockOnCancel} />);
+      fireEvent.click(screen.getByText('Email'));
+
+      fireEvent.change(screen.getByPlaceholderText('user@example.com or API key'), {
+        target: { value: 'apikey' },
+      });
+      fireEvent.change(document.querySelector('input[type="password"]')!, {
+        target: { value: 'secret' },
+      });
+      fireEvent.change(screen.getByPlaceholderText('smtp.example.com'), {
+        target: { value: 'smtp.postmarkapp.com' },
+      });
+      // port left blank (optional)
+      fireEvent.change(screen.getByPlaceholderText('noreply@example.com'), {
+        target: { value: 'noreply@example.com' },
+      });
+      fireEvent.change(screen.getByPlaceholderText('you@example.com'), {
+        target: { value: 'me@example.com' },
+      });
+
+      fireEvent.click(screen.getByText('Next').closest('button')!);
+      fireEvent.change(screen.getByPlaceholderText('e.g. My Telegram Alert'), {
+        target: { value: 'Postmark' },
+      });
+      fireEvent.click(screen.getByText('Save Channel').closest('button')!);
+
+      const url = mockOnComplete.mock.calls[0][0].apprise_url as string;
+      expect(url).toContain('mailto://apikey:secret@smtp.postmarkapp.com/');
+      expect(url).toContain('to=me%40example.com');
+      expect(url).toContain('from=noreply%40example.com');
+    });
   });
 
   // ── Edit mode (initialData) ────────────────────────────────────────────

frontend/src/components/NotificationWizard.tsx

@@ -71,10 +71,28 @@ const CHANNEL_FIELDS: Record<string, ChannelField[]> = {
     },
   ],
   email: [
-    { key: 'username', label: 'Username / Email', placeholder: 'user@example.com' },
+    {
+      key: 'username',
+      label: 'SMTP Username',
+      placeholder: 'user@example.com or API key',
+      hint: 'SMTP authentication username — can be an API key (e.g. Postmark)',
+    },
     { key: 'password', label: 'SMTP Password', placeholder: '••••••••', type: 'password' },
     { key: 'host', label: 'SMTP Host', placeholder: 'smtp.example.com' },
     { key: 'port', label: 'SMTP Port', placeholder: '587', optional: true },
+    {
+      key: 'sender',
+      label: 'Sender Email (From)',
+      placeholder: 'noreply@example.com',
+      hint: 'Email address shown as the sender. Defaults to SMTP Username if blank.',
+      optional: true,
+    },
+    {
+      key: 'recipient',
+      label: 'Recipient Email (To)',
+      placeholder: 'you@example.com',
+      hint: 'Email address where notifications are delivered.',
+    },
   ],
   webhook: [
     {
@@ -113,11 +131,15 @@ function buildAppriseUrl(channel: string, fields: Record<string, string>): strin
       if (match) return `slack://${match[1]}/${match[2]}/${match[3]}/`;
       return '';
     }
-    case 'email':
-      if (!fields.username || !fields.password || !fields.host) return '';
+    case 'email': {
+      if (!fields.username || !fields.password || !fields.host || !fields.recipient) return '';
+      const params = new URLSearchParams();
+      params.set('to', fields.recipient);
+      if (fields.sender) params.set('from', fields.sender);
       return `mailto://${encodeURIComponent(fields.username)}:${encodeURIComponent(fields.password)}@${fields.host}${
         fields.port ? `:${fields.port}` : ''
-      }`;
+      }/?${params.toString()}`;
+    }
     case 'webhook':
       return fields.url || '';
     case 'custom':