Can someone at least tell me why this question is not being answered. I've seen it asked so many times before and, this is the second time asking it myself. Thanks.

Are these local calendars, or network calendars, such as Google Calendar?

I'm asking because if you want to use email reminders, it's important to understand who or what sends them. If it's a local calendar then only Thunderbird can send them, and this won't happen if it isn't open, running and connected to the Internet. If it's a network calendar, you need to ascertain if it supports email reminders.

I don't use email for critical things because it isn't real time and isn't dependable. I've seen email messages delayed by minutes, hours or even days. Using the alternative notification and a network calendar means that I'll get reminders on phone, tablet and pc.

Thanks for the walk through. Honestly, I don't know which it is. It's the calendar add on to Thunderbird Email program called "Lightning". I did a few tests the past few hours, creating test events and setting reminders to show up in 5 minutes and then one for 30 minutes and, I had the Email and Calendar program open and was connected to the internet when the reminder was supposed to show up but, none of them did. Funny, I got a reminder yesterday for an event I deleted 3 months ago. Mystery. Anyhow, thanks for taking the time to try to help me. I'm like you, at least since this started happening. Can't leave important reminders up to a Calendar that is not reliable.

You're almost certainly using a local calendar then. That's the default in Lightning.

To use a networked calendar, you have to either jump through hoops to discover and insert the appropriate calendar URL, or install an add-on. You haven't mentioned any of this, so I take it you're using the default built in local calendar.

If you were to use Google Calendar, then you would would be delegating the job of issuing reminders to their server, and this takes Thunderbird/Lightning almost totally out of the loop, once you have set up the event.

I wasn't trying to say that the calendar (Lightning) is unreliable, but rather that the use of email to issue notifications isn't reliable. If I'm not actually sitting in front of my PC with an email client up and running, I'm not going to see email notifications anyway. But use Google Calendar and Android and your phone or tablet will get notifications. More importantly, when you set up an event, it will be transferred to the server and from there to individual devices, so they can operate autonomously and generate their own notifications. I presume Apple enthusiasts will have something similar in their own parallel universe.

Google Calendar is the path of least resistance with Lightning. There is an add-on that makes linking up Lightning to Google Calendar very simple to set up. If you don't like add-ons, then you can also connect to Google Calendar using the built-in support for CalDAV.

Other calendars are available, but in general they are not so easy to set up. I also use a calendar provided by an email provider (gmx.com) using CalDAV, and another using an ics file via DropBox, but both of these are only accessible via Lightning in Thunderbird (or their own webpage); there's no way I have found to get them to connect to an Android phone. To be fair, the gmx one does send me emails to remind me of events, but then that is their server doing the sending and it is pretty well detached from Thunderbird/Lightning. And I still have reservations about relying on email for time-sensitive activities.

I do appreciate all the time you spent on this trying to help. I did go for the google calendar idea. Created a calendar there and then I installed the google calendar ad on in Lightening, I created an event but still no email reminders. Searched and learned a lot from google websites about changing settings and getting email notifications etc. but, no dice. Spent too much time already on this matter. Thanks anyway. I'll just live w/o reminders. But, I am really surprised at how many posts I see on the internet about this very matter but no real answers on this simple question. "Why we used to get email reminders and now we don't." If they are no longer available, just let us know. (not you Zenos. you've been so kind to take this time with me.)