When Not to Send iCal Invitations

Making travel reservations online has come a long way, and some airlines now even include standard vCalendar files in their confirmation emails, so it takes just a few mouse clicks to add all flight-related information to your digital calendar. One such airlines is Lufthansa, who include vCalendar invitations. And that, I daresay, is a bad idea.

From a user's point of view, there are two main types of vCalendar events: published events and invitation events. (For more on the technical details, have a look at the vCalendar entry on Wikipedia and, more specifically, RFC2446 on "iCalendar Transport-Independent Interoperability").

Choosing a target calendar for a published event.

Double-clicking a vCalendar file on a Mac will open iCal for adding the event defined in that file. In the case of a published event, iCal will simply ask to which of your iCal calendars the event should be added. Select one, click OK, and you're done.

New invitation events are listed in iCal's Notification panel, and numbers in the Calendars panel show their number for the respective calendar.

In the case of an invitation event, however, there's more to it: iCal presents the Edit view of the event, displaying three buttons at the bottom: "Maybe," "Decline," "Accept." Until you click any of these buttons, the event is grayed out in the calendar and remains listed in iCal's Notifications panel. The number of open invitations is also displayed next to the target calendar in the Calendars list, and iCal's icon shows the sum of all new invitations, too.

Once you do reply to the invitation, the event is added to the target calendar and, in the background, iCal triggers an email with your decision to be sent to the email address listed under "Organizer" in the event.

Editing invitation events is highly limited, as all you can do is choose the calendar to add them to, and create alarms for the event. You cannot, however, edit any other data fields, including notes, and when you try to move the event, you'll see an error message. In general, these limitations do make sense to keep the event's details synchronized and coherent for all invitees.

Trying to move an invitation event results in an error.

So, why is it a bad idea for Lufthansa to send out invitation events with their flight confirmation emails? Most importantly, like any other invitation, these ones also create email messages with your replies, in this case to ics@pcsoffice.de, which, incidentally, bounces due to an unknown account. Why should an event with flight information "phone home" when you add it to your calendar, especially to an address that, at first sight, is not even related to the airline?

In case I choose to not reply at all, however, these events will clog my Notifications list indefinitely, or until I delete them, either of which makes for an unnecessary nuisance. Furthermore, I cannot add any additional information I might find useful to the Notes field and -- in this specific case -- the events also lack time zone information. Instead, the events are scheduled for the respective local times for departure and arrival, so that the flight durations are distorted for routes that cross time zones.

The vCalendar event files that the Lufthansa airline includes with their confirmation emails contains lots of useful information way beyond just the flight times. If only it were not packaged as an invitation.

Lufthansa should just have used simple vCalendar event publications, allowing editing of the events and doing away with the potential security hole of "phoning home."

As a rule of thumb, only use vCalendar invitations if you do require a reply from the recipient about whether she will participate or not, or if you need to make absolutely sure that the user cannot edit the event in their calendar. In all other cases -- e.g., to share travel itineraries, class schedules, etc. --, sticking with standard vCalendar published event files should do the trick just fine: just drag and drop the event from iCal into a Finder window or an email message, et voilà!