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)

src/i18n/de.json

@@ -644,9 +644,11 @@
     "invitationPending": "Einladung ausstehend",
     "pendingInvitations": "Ausstehende Einladungen",
     "accepted": "Angenommen",
-    "sendFederated": "An Remote senden",
+    "sendFederated": "Remote einladen",
-    "sendFederatedTitle": "Event an Remote-Instanz senden",
+    "sendFederatedTitle": "Termin-Einladung senden",
-    "sendFederatedDesc": "Sende dieses Kalender-Event an einen Benutzer auf einer anderen Redlight-Instanz. Der Empfänger muss die Einladung zuerst annehmen, bevor das Event in seinem Kalender erscheint.",
+    "sendFederatedDesc": "Sende dieses Kalender-Event an einen Benutzer auf einer anderen Redlight-Instanz oder an eine beliebige E-Mail-Adresse. Remote-Empfänger müssen die Einladung zuerst annehmen, bevor das Event in ihrem Kalender erscheint; E-Mail-Empfänger erhalten die Termindetails mit einer .ics-Datei im Anhang.",
+    "inviteSection": "Einladungen versenden (optional)",
+    "inviteSectionHint": "Lade Personen per E-Mail ein oder sende das Event an einen Benutzer auf einer anderen Redlight-Instanz.",
     "send": "Senden",
     "fedSent": "Kalendereinladung gesendet! Der Empfänger muss diese zuerst annehmen.",
     "fedFailed": "Event konnte nicht an Remote-Instanz gesendet werden",

src/i18n/en.json

@@ -644,9 +644,11 @@
     "invitationPending": "Invitation pending",
     "pendingInvitations": "Pending Invitations",
     "accepted": "Accepted",
-    "sendFederated": "Send to remote",
+    "sendFederated": "Invite remote",
-    "sendFederatedTitle": "Send Event to Remote Instance",
+    "sendFederatedTitle": "Send Event Invitation",
-    "sendFederatedDesc": "Send this calendar event to a user on another Redlight instance. The recipient must accept the invitation before the event appears in their calendar.",
+    "sendFederatedDesc": "Send this calendar event to a user on another Redlight instance or to any email address. Remote recipients must accept the invitation before the event appears in their calendar; email recipients receive the event details with an .ics attachment.",
+    "inviteSection": "Send invitations (optional)",
+    "inviteSectionHint": "Invite people by email or send the event to a user on another Redlight instance.",
     "send": "Send",
     "fedSent": "Calendar invitation sent! The recipient must accept it first.",
     "fedFailed": "Could not send event to remote instance",

src/pages/Calendar.jsx

@@ -42,8 +42,13 @@ export default function Calendar() {
   const [sharedUsers, setSharedUsers] = useState([]);
   const [pendingInvitations, setPendingInvitations] = useState([]);
   const [fedAddress, setFedAddress] = useState('');
+  const [fedEmails, setFedEmails] = useState('');
   const [fedSending, setFedSending] = useState(false);
 
+  // Invitations sent right after creating an event
+  const [inviteFedAddress, setInviteFedAddress] = useState('');
+  const [inviteEmails, setInviteEmails] = useState('');
+
   // Load events on month change
   useEffect(() => {
     fetchEvents();
@@ -159,6 +164,8 @@ export default function Calendar() {
       end_time: toLocalDateTimeStr(end),
       room_uid: '', color: '#6366f1', reminder_minutes: null,
     });
+    setInviteFedAddress('');
+    setInviteEmails('');
     setEditingEvent(null);
     setShowCreate(true);
   };
@@ -178,8 +185,41 @@ export default function Calendar() {
     setShowCreate(true);
   };
 
+  const isValidFedAddress = (address) => {
+    const normalized = address.startsWith('@') ? address.slice(1) : address;
+    return normalized.includes('@') && !normalized.endsWith('@');
+  };
+
+  // Send invitations for an event; shows a toast per outcome (non-fatal on failure)
+  const sendEventInvites = async (eventId, address, emailsStr) => {
+    const addr = address.trim();
+    if (addr) {
+      try {
+        await api.post(`/calendar/events/${eventId}/federation`, { to: addr });
+        toast.success(t('calendar.fedSent'));
+      } catch (err) {
+        toast.error(err.response?.data?.error || t('calendar.fedFailed'));
+      }
+    }
+    const emailList = emailsStr.split(',').map(s => s.trim()).filter(Boolean);
+    if (emailList.length > 0) {
+      try {
+        await api.post(`/calendar/events/${eventId}/email`, { emails: emailList });
+        toast.success(t('federation.emailSent'));
+      } catch (err) {
+        toast.error(err.response?.data?.error || t('federation.emailSendFailed'));
+      }
+    }
+  };
+
   const handleSave = async (e) => {
     e.preventDefault();
+
+    if (!editingEvent && inviteFedAddress.trim() && !isValidFedAddress(inviteFedAddress.trim())) {
+      toast.error(t('federation.addressHint'));
+      return;
+    }
+
     setSaving(true);
     try {
       const data = {
@@ -192,11 +232,17 @@ export default function Calendar() {
         await api.put(`/calendar/events/${editingEvent.id}`, data);
         toast.success(t('calendar.eventUpdated'));
       } else {
-        await api.post('/calendar/events', data);
+        const res = await api.post('/calendar/events', data);
         toast.success(t('calendar.eventCreated'));
+        const created = res.data.event;
+        if (created && (inviteFedAddress.trim() || inviteEmails.trim())) {
+          await sendEventInvites(created.id, inviteFedAddress, inviteEmails);
+        }
       }
       setShowCreate(false);
       setEditingEvent(null);
+      setInviteFedAddress('');
+      setInviteEmails('');
       fetchEvents();
     } catch (err) {
       toast.error(err.response?.data?.error || t('calendar.saveFailed'));
@@ -328,19 +374,41 @@ export default function Calendar() {
   const handleFedSend = async (e) => {
     e.preventDefault();
     if (!showFedShare) return;
-    const normalized = fedAddress.startsWith('@') ? fedAddress.slice(1) : fedAddress;
+    const hasAddress = fedAddress.trim().length > 0;
-    if (!normalized.includes('@') || normalized.endsWith('@')) {
+    const hasEmails = fedEmails.trim().length > 0;
+
+    if (!hasAddress && !hasEmails) {
       toast.error(t('federation.addressHint'));
       return;
     }
+
     setFedSending(true);
     try {
-      await api.post(`/calendar/events/${showFedShare.id}/federation`, { to: fedAddress });
+      if (hasAddress) {
-      toast.success(t('calendar.fedSent'));
+        // Federation address mode
+        if (!isValidFedAddress(fedAddress.trim())) {
+          toast.error(t('federation.addressHint'));
+          setFedSending(false);
+          return;
+        }
+        await api.post(`/calendar/events/${showFedShare.id}/federation`, { to: fedAddress });
+        toast.success(t('calendar.fedSent'));
+      } else {
+        // Email mode
+        const emailList = fedEmails.split(',').map(s => s.trim()).filter(Boolean);
+        if (emailList.length === 0) {
+          toast.error(t('federation.emailHint'));
+          setFedSending(false);
+          return;
+        }
+        await api.post(`/calendar/events/${showFedShare.id}/email`, { emails: emailList });
+        toast.success(t('federation.emailSent'));
+      }
       setShowFedShare(null);
       setFedAddress('');
+      setFedEmails('');
     } catch (err) {
-      toast.error(err.response?.data?.error || t('calendar.fedFailed'));
+      toast.error(err.response?.data?.error || t(hasAddress ? 'calendar.fedFailed' : 'federation.emailSendFailed'));
     } finally {
       setFedSending(false);
     }
@@ -378,6 +446,8 @@ export default function Calendar() {
             end_time: toLocalDateTimeStr(end),
             room_uid: '', color: '#6366f1',
           });
+          setInviteFedAddress('');
+          setInviteEmails('');
           setEditingEvent(null);
           setShowCreate(true);
         }} className="btn-primary">
@@ -616,6 +686,41 @@ export default function Calendar() {
               </div>
             </div>
 
+            {!editingEvent && (
+              <div className="pt-4 border-t border-th-border space-y-4">
+                <div>
+                  <p className="text-sm font-medium text-th-text">{t('calendar.inviteSection')}</p>
+                  <p className="text-xs text-th-text-s mt-0.5">{t('calendar.inviteSectionHint')}</p>
+                </div>
+
+                <div>
+                  <label htmlFor="calendar-invite-emails" className="block text-sm font-medium text-th-text mb-1.5">{t('federation.emailLabel')}</label>
+                  <input
+                    id="calendar-invite-emails"
+                    type="text"
+                    value={inviteEmails}
+                    onChange={e => setInviteEmails(e.target.value)}
+                    className="input-field"
+                    placeholder={t('federation.emailPlaceholder')}
+                  />
+                  <p className="text-xs text-th-text-s mt-1">{t('federation.emailHint')}</p>
+                </div>
+
+                <div>
+                  <label htmlFor="calendar-invite-fed-address" className="block text-sm font-medium text-th-text mb-1.5">{t('federation.addressLabel')}</label>
+                  <input
+                    id="calendar-invite-fed-address"
+                    type="text"
+                    value={inviteFedAddress}
+                    onChange={e => setInviteFedAddress(e.target.value)}
+                    className="input-field"
+                    placeholder={t('federation.addressPlaceholder')}
+                  />
+                  <p className="text-xs text-th-text-s mt-1">{t('federation.addressHint')}</p>
+                </div>
+              </div>
+            )}
+
             <div className="flex items-center gap-3 pt-4 border-t border-th-border">
               <button type="button" onClick={() => { setShowCreate(false); setEditingEvent(null); }} className="btn-secondary flex-1">
                 {t('common.cancel')}
@@ -827,9 +932,9 @@ export default function Calendar() {
         </Modal>
       )}
 
-      {/* Federation Share Modal */}
+      {/* Federation/Email Share Modal */}
       {showFedShare && (
-        <Modal title={t('calendar.sendFederatedTitle')} onClose={() => setShowFedShare(null)}>
+        <Modal title={t('calendar.sendFederatedTitle')} onClose={() => { setShowFedShare(null); setFedAddress(''); setFedEmails(''); }}>
           <p className="text-sm text-th-text-s mb-4">{t('calendar.sendFederatedDesc')}</p>
           <form onSubmit={handleFedSend} className="space-y-4">
             <div>
@@ -838,18 +943,39 @@ export default function Calendar() {
                 id="calendar-fed-share-address"
                 type="text"
                 value={fedAddress}
-                onChange={e => setFedAddress(e.target.value)}
+                onChange={e => { setFedAddress(e.target.value); if (e.target.value) setFedEmails(''); }}
                 className="input-field"
                 placeholder={t('federation.addressPlaceholder')}
-                required
+                disabled={fedEmails.trim().length > 0}
               />
               <p className="text-xs text-th-text-s mt-1">{t('federation.addressHint')}</p>
             </div>
+
+            <div className="flex items-center gap-3 my-2">
+              <div className="flex-1 border-t border-th-border" />
+              <span className="text-xs text-th-text-s uppercase">{t('common.or')}</span>
+              <div className="flex-1 border-t border-th-border" />
+            </div>
+
+            <div>
+              <label htmlFor="calendar-fed-share-emails" className="block text-sm font-medium text-th-text mb-1.5">{t('federation.emailLabel')}</label>
+              <input
+                id="calendar-fed-share-emails"
+                type="text"
+                value={fedEmails}
+                onChange={e => { setFedEmails(e.target.value); if (e.target.value) setFedAddress(''); }}
+                className="input-field"
+                placeholder={t('federation.emailPlaceholder')}
+                disabled={fedAddress.trim().length > 0}
+              />
+              <p className="text-xs text-th-text-s mt-1">{t('federation.emailHint')}</p>
+            </div>
+
             <div className="flex items-center gap-3 pt-2 border-t border-th-border">
-              <button type="button" onClick={() => setShowFedShare(null)} className="btn-secondary flex-1">
+              <button type="button" onClick={() => { setShowFedShare(null); setFedAddress(''); setFedEmails(''); }} className="btn-secondary flex-1">
                 {t('common.cancel')}
               </button>
-              <button type="submit" disabled={fedSending} className="btn-primary flex-1">
+              <button type="submit" disabled={fedSending || (!fedAddress.trim() && !fedEmails.trim())} className="btn-primary flex-1">
                 {fedSending ? <Loader2 size={16} className="animate-spin" /> : <Send size={16} />}
                 {t('calendar.send')}
               </button>