feat: send calendar event invitations by email or federation

- New endpoint POST /api/calendar/events/:id/email sends event
  invitations with an .ics attachment to external email addresses
  (rate-limited like room email invites)
- Create-event dialog gets an optional invitations section to invite
  people by email or federation address right away
- The "Invite remote" dialog on existing events now accepts email
  addresses in addition to federation IDs

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/config/mailer.js

@@ -289,6 +289,78 @@ export async function sendCalendarInviteEmail(to, name, fromUser, title, startTi
   });
 }
 
+/**
+ * Send a calendar event invitation to an external email address (with ICS attachment).
+ * @param {string} to          - recipient email
+ * @param {string} fromUser    - sender display name
+ * @param {string} title       - event title
+ * @param {string} startTime   - ISO start time
+ * @param {string} endTime     - ISO end time
+ * @param {string|null} description - optional event description
+ * @param {string|null} joinUrl - direct meeting join URL if a room is linked
+ * @param {string} ics         - ICS file content to attach
+ * @param {string} appName     - branding app name
+ * @param {string} lang        - language code
+ */
+export async function sendCalendarEventEmail(to, fromUser, title, startTime, endTime, description, joinUrl, ics, appName = 'Redlight', lang = 'en') {
+  if (!transporter) {
+    throw new Error('SMTP not configured');
+  }
+
+  const from = process.env.SMTP_FROM || process.env.SMTP_USER;
+  const headerAppName = sanitizeHeaderValue(appName);
+  const safeFromUser = escapeHtml(fromUser);
+  const safeTitle = escapeHtml(title);
+  const safeDesc = description ? escapeHtml(description) : null;
+
+  const formatDate = (iso) => {
+    try { return new Date(iso).toLocaleString(lang === 'de' ? 'de-DE' : 'en-GB', { dateStyle: 'full', timeStyle: 'short' }); }
+    catch { return iso; }
+  };
+
+  const introHtml = t(lang, 'email.calendarEventInvite.intro')
+    .replace('{fromUser}', `<strong style="color:#cdd6f4;">${safeFromUser}</strong>`);
+
+  await transporter.sendMail({
+    from: `"${headerAppName}" <${from}>`,
+    to,
+    subject: t(lang, 'email.calendarEventInvite.subject', { appName: headerAppName, title: sanitizeHeaderValue(title) }),
+    html: `
+      <div style="font-family:Arial,sans-serif;max-width:520px;margin:0 auto;padding:32px;background:#1e1e2e;color:#cdd6f4;border-radius:12px;">
+        <h2 style="color:#cba6f7;margin-top:0;">${t(lang, 'email.calendarEventInvite.title')}</h2>
+        <p>${introHtml}</p>
+        <div style="background:#313244;border-radius:8px;padding:16px;margin:20px 0;">
+          <p style="margin:0 0 4px 0;font-size:15px;font-weight:bold;color:#cdd6f4;">${safeTitle}</p>
+          <p style="margin:6px 0 0 0;font-size:13px;color:#a6adc8;">${escapeHtml(formatDate(startTime))} - ${escapeHtml(formatDate(endTime))}</p>
+          ${safeDesc ? `<p style="margin:10px 0 0 0;font-size:13px;color:#a6adc8;font-style:italic;">&quot;${safeDesc}&quot;</p>` : ''}
+        </div>
+        ${joinUrl ? `
+        <p style="text-align:center;margin:28px 0;">
+          <a href="${joinUrl}"
+             style="display:inline-block;background:#cba6f7;color:#1e1e2e;padding:12px 32px;border-radius:8px;text-decoration:none;font-weight:bold;">
+            ${t(lang, 'email.calendarEventInvite.joinButton')}
+          </a>
+        </p>
+        <p style="font-size:13px;color:#7f849c;">
+          ${t(lang, 'email.linkHint')}<br/>
+          <a href="${joinUrl}" style="color:#89b4fa;word-break:break-all;">${escapeHtml(joinUrl)}</a>
+        </p>` : ''}
+        <p style="font-size:13px;color:#7f849c;">${t(lang, 'email.calendarEventInvite.icsHint')}</p>
+        <hr style="border:none;border-top:1px solid #313244;margin:24px 0;"/>
+        <p style="font-size:12px;color:#585b70;">${t(lang, 'email.calendarEventInvite.footer', { appName: escapeHtml(appName) })}</p>
+      </div>
+    `,
+    text: `${t(lang, 'email.calendarEventInvite.intro', { fromUser })}\n${title}\n${formatDate(startTime)} – ${formatDate(endTime)}${description ? `\n\n"${description}"` : ''}${joinUrl ? `\n\n${t(lang, 'email.calendarEventInvite.joinButton')}: ${joinUrl}` : ''}\n\n${t(lang, 'email.calendarEventInvite.icsHint')}\n\n– ${appName}`,
+    attachments: [
+      {
+        filename: 'event.ics',
+        content: ics,
+        contentType: 'text/calendar; charset=utf-8; method=PUBLISH',
+      },
+    ],
+  });
+}
+
 /**
  * Notify a user that a federated calendar event they received was deleted by the organiser.
  */

server/i18n/de.json

@@ -43,6 +43,14 @@
       "subject": "{appName} - Kalendereinladung von {fromUser}",
       "intro": "Du hast eine Kalendereinladung von {fromUser} erhalten."
     },
+    "calendarEventInvite": {
+      "subject": "{appName} - Kalendereinladung: {title}",
+      "title": "Kalendereinladung",
+      "intro": "{fromUser} hat dich zu folgendem Termin eingeladen:",
+      "joinButton": "Meeting beitreten",
+      "icsHint": "Mit der angehängten .ics-Datei kannst du den Termin zu deinem Kalender hinzufügen.",
+      "footer": "Diese Einladung wurde über {appName} versendet."
+    },
     "calendarDeleted": {
       "subject": "{appName} - Kalendereintrag abgesagt: {title}",
       "intro": "Der folgende Kalendereintrag wurde vom Organisator ({fromUser}) gelöscht und ist nicht mehr verfügbar:",

server/i18n/en.json

@@ -43,6 +43,14 @@
       "subject": "{appName} - Calendar invitation from {fromUser}",
       "intro": "You have received a calendar invitation from {fromUser}."
     },
+    "calendarEventInvite": {
+      "subject": "{appName} - Calendar invitation: {title}",
+      "title": "Calendar Invitation",
+      "intro": "{fromUser} has invited you to the following event:",
+      "joinButton": "Join Meeting",
+      "icsHint": "You can add this event to your calendar using the attached .ics file.",
+      "footer": "This invitation was sent via {appName}."
+    },
     "calendarDeleted": {
       "subject": "{appName} - Calendar event cancelled: {title}",
       "intro": "The following calendar event was deleted by the organiser ({fromUser}) and is no longer available:",

server/routes/calendar.js

@@ -3,7 +3,7 @@ import crypto from 'crypto';
 import { getDb } from '../config/database.js';
 import { authenticateToken, getBaseUrl } from '../middleware/auth.js';
 import { log } from '../config/logger.js';
-import { sendCalendarInviteEmail } from '../config/mailer.js';
+import { sendCalendarInviteEmail, sendCalendarEventEmail } from '../config/mailer.js';
 import { getAppName } from '../config/appName.js';
 import {
   isFederationEnabled,
@@ -23,6 +23,16 @@ const SAFE_COLOR_RE = /^(?:#[0-9a-fA-F]{3,8}|hsl\(\d{1,3},\s*\d{1,3}%,\s*\d{1,3}
 // Allowed reminder intervals in minutes
 const VALID_REMINDERS = new Set([5, 15, 30, 60, 120, 1440]);
 
+// Rate limit email invitations: each request may carry up to 50 addresses, so
+// without a cap any registered account could be abused as an SMTP spam relay.
+const calendarEmailInviteLimiter = rateLimit({
+  windowMs: 60 * 60 * 1000, // 1 hour
+  max: 10,
+  standardHeaders: true,
+  legacyHeaders: false,
+  message: { error: 'Too many email invitations. Please try again later.' },
+});
+
 // Rate limit for federation calendar receive
 const calendarFederationLimiter = rateLimit({
   windowMs: 15 * 60 * 1000,
@@ -581,6 +591,69 @@ router.post('/events/:id/federation', authenticateToken, async (req, res) => {
   }
 });
 
+// ── POST /api/calendar/events/:id/email — Send event invitation by email ────
+router.post('/events/:id/email', authenticateToken, calendarEmailInviteLimiter, async (req, res) => {
+  try {
+    const { emails } = req.body;
+    if (!emails || !Array.isArray(emails) || !emails.length) {
+      return res.status(400).json({ error: 'At least one email address is required' });
+    }
+    if (emails.length > 50) {
+      return res.status(400).json({ error: 'Maximum 50 email addresses allowed' });
+    }
+
+    const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+    for (const email of emails) {
+      if (typeof email !== 'string' || !emailRegex.test(email) || email.length > 254) {
+        return res.status(400).json({ error: `Invalid email address: ${email}` });
+      }
+    }
+
+    const db = getDb();
+    const event = await db.get(`
+      SELECT ce.*, COALESCE(NULLIF(u.display_name,''), u.name) as organizer_name, u.email as organizer_email
+      FROM calendar_events ce
+      JOIN users u ON ce.user_id = u.id
+      WHERE ce.id = ? AND ce.user_id = ?
+    `, [req.params.id, req.user.id]);
+    if (!event) return res.status(404).json({ error: 'Event not found or no permission' });
+
+    const baseUrl = getBaseUrl(req);
+    let joinUrl = null;
+    if (event.room_uid) {
+      joinUrl = `${baseUrl}/join/${event.room_uid}`;
+    }
+
+    const ics = generateICS(event, joinUrl || '', baseUrl);
+    const appName = await getAppName();
+    const fromUser = req.user.display_name || req.user.name;
+    const lang = req.user.language || 'en';
+
+    // Send emails (in parallel but collect errors)
+    const results = await Promise.allSettled(
+      emails.map(email =>
+        sendCalendarEventEmail(
+          email, fromUser, event.title, event.start_time, event.end_time,
+          event.description, joinUrl, ics, appName, lang
+        )
+      )
+    );
+
+    const failed = results.filter(r => r.status === 'rejected');
+    if (failed.length === emails.length) {
+      return res.status(500).json({ error: 'Failed to send all email invitations' });
+    }
+    if (failed.length > 0) {
+      log.server.warn(`${failed.length}/${emails.length} calendar email invitations failed`);
+    }
+
+    res.json({ success: true, sent: emails.length - failed.length, failed: failed.length });
+  } catch (err) {
+    log.server.error(`Calendar email invite error: ${err.message}`);
+    res.status(500).json({ error: err.message || 'Failed to send email invitations' });
+  }
+});
+
 // ── POST /receive-event or /calendar-event — Receive calendar event from remote ──
 // '/receive-event' when mounted at /api/calendar
 // '/calendar-event' when mounted at /api/federation (for remote instance discovery)