It doesn't support the use of email reminders. They wouldn't be reliable. Email isn't real time. And who would send the email? What if you're in an area with no network coverage? If you're using Thunderbird or a calendar app that synchronises to the same calendar you'll get a pop-up notification at the alarm time. If you're not using Thunderbird at the due time, it can't send the reminder. You need the server hosting your calendar to send this postulated email reminder. You apparently have this facility but Lightning doesn't support it.

What Thunderbird/Lightning can do is send invitations by email, and the invitation, in a rationally designed system, would have a simple method whereby you add it to your own calendar.

Hi, thank you for your answer.

I don't want Thunderbird to actually *send* these emails - just to put a proper value in an event's description.

My calendar server is set up to send e-mail reminders if the event is configured to do so.

EMAIL reminder action is defined in RFC 4791, page 76, so it would be super-cool if I could configure that option right from within Lightning :)