How to specify the e-mail account Thunderbird uses to reply to event invitations

Usually applications with a GUI are intuitive to use and not too difficult to configure. But sometimes I end up banging my head against a brick wall. Such was the case when I wanted to change the default e-mail account that the Thunderbird e-mail client uses to send an ‘Email Notification’ in reply to a meeting invitation.

I have several e-mail accounts and use Thunderbird with the Lightning calendar extension. When my e-mail accounts receive a meeting invitiation e-mail, the row of buttons ‘Accept’, ‘Tentative’ and ‘Decline’ is displayed at the top of the invitation window. The problem is that, whichever of my e-mail accounts receives an event invitation e-mail, clicking on the aforementioned buttons always results in Thunderbird sending the reply (‘Event Notification Email’) from a fixed e-mail account. To give a hypothetical example, let’s say I had the e-mail accounts cfitzcarrald@iquitos.pe, c.f.fitzcarrald@caucho.co.pe, cff@puertomaldonado.com and carlosffitzcarrald@hotmail.com. Whichever of those accounts receives an event invitation e-mail, when I click on ‘Accept’ the reply is always sent from the account cfitzcarrald@iquitos.pe.

It turns out that the e-mail account Thunderbird uses to send event notification replies is tied to the calendar, not to the e-mail account which received the invitation (see Mozilla Bugzilla Bug No. 589081 – Wrong outgoing server for meet confirmation in Lighting plugin for Thunderbird). However, it is not obvious how to specify the default e-mail account to be used by the calendar, so here is how to do it in Thunderbird 31.2.0 and Lightning 3.3.2:

1. There are two icons at the top right of the Thunderbird window in my case: a calendar icon and a clipboard icon. Hovering the mouse pointer over those two icons displays the tooltips ‘Switch to the calendar tab’ and ‘Switch to the tasks tab’ respectively. Click on the calendar icon to display the calendar tab.
2. The calendar tab should be displayed. Click on ‘Edit’ and select ‘Calendar Properties…’ from the drop-down menu. A window titled ‘Edit Calendar’ should pop up.
3. In the ‘Edit Calendar’ window, select the default e-mail account from the drop-down menu of e-mail accounts, make sure ‘Read Only’ is not ticked, and click ‘OK’.

That’s all there is to it. It is a pity the Thunderbird UI does not make it at all obvious how to do it.