Summary /////////////////////////////////////////////////////////

Add full support for standard calendar event invitations so recipients receive actionable event requests (Accept / Decline / Tentative) instead of a passive .ics attachment.

Description /////////////////////////////////////////////////////////

When adding participants to a Proton Calendar event, recipients currently receive an email containing an .ics file. However, this does not appear as a proper event invitation in many calendar clients and does not offer standard response options such as Accept, Decline, or Tentative.

As a result, the event is not treated as a true meeting request but rather as a file attachment, which significantly limits usability.

Problems / Impact /////////////////////////////////////////////////////////

• No standardized RSVP workflow
• No visibility into participant responses
• Manual follow-up required
• Poor interoperability with common calendar systems
• Not suitable for business or professional use
• Creates the impression that the sender is using a non-standard or outdated solution

For business communication in particular, this is a serious limitation. It also affects private use, where users expect
basic RSVP functionality to “just work.”

Business & Trust Impact /////////////////////////////////////////////////////////

Because invitations don’t behave like standard meeting requests, it unintentionally signals to recipients that the sender is not using a “normal” or widely adopted calendar system (e.g. Microsoft 365, Google Calendar). This can undermine professional credibility and confidence, even though the issue is purely technical.

Proposed Solution /////////////////////////////////////////////////////////

Implement full iCalendar (RFC 5545 / 5546) invitation support, including:
- Proper meeting request emails
- Accept / Decline / Tentative actions in recipients’ calendars
- Automatic response handling
- Organizer visibility of attendee status
- Updates and cancellations that sync correctly

Expected Outcome /////////////////////////////////////////////////////////

• Invitations behave like standard calendar events across platforms
• Seamless interoperability with Outlook, Apple Calendar, Google Calendar, etc.
• Proton Calendar becomes viable for business and professional scheduling

Priority Justification /////////////////////////////////////////////////////////
Meeting invitations are a core calendar feature. Without proper RSVP handling, Proton Calendar cannot realistically replace mainstream calendar solutions for business or serious private use.