Thunderbird reminder alarms
Solution 1:
Note: This answer is now of only historical value. It was updated in November 2019 to reflect the developers dropping support for Mozilla products other than Thunderbird, and their intention to not support Thunderbird v65 and beyond. User s3c reported testing with Thunderbird v68.5 and confirmed that it no longer works.
This type of email reminder isn't a native feature of Thunderbird, it requires an add-on. I actually went looking for one after your question made me realize I needed the same thing.
ReminderFox
ReminderFox appears to be generally recognized as the reminder program for Thunderbird and other Mozilla products, and it's free. I've just loaded this add-on, myself, and haven't yet had much chance to become real familiar with it. But I've tested the basics and am very impressed.
ReminderFox is actually a complete calendar / to-do / list application that does email reminders as part of its repertoire. Its list of features and capabilities is extensive. I've just scratched the surface, myself. They have a series of short tutorial videos that will give you a feel for what it can do. I'll focus here on just the email reminders.
Installing it
It integrates with Thunderbird or any of the Mozilla email or browser products. For example, you can load it on Firefox and use it to do reminders directly on your web mail.
A download link for Thunderbird is here. You can install it on Firefox from a tab on their web site (first link in this answer). However, probably the easiest way to install it in Thunderbird or other Mozilla products is to go to the app's add-ons page, enter reminderfox in the search box, and install it from there.
Using it
The documentation is pretty thorough. The instructions for using it as a message reminder (what you asked) is included there.
There are endless options. You can attach a reminder to a message when you send it, as well as to messages you have received.
It adds a selection to the context menu. So right-clicking on a message gives you the item near the bottom:
Clicking that opens the add event dialog, which will give you an idea of the options:
Some of the features:
- You can view an email from the reminder.
- If an email with an associated reminder is replied to, the reply will also contain a reference to this reminder.
- If you make extensive use of ReminderFox and want a tool to simplify organizing and finding the messages, it includes tagging, filtering, and searching.
The actual email reminders are somewhat similar to the calendar reminders that pop up when you use Lightning.
Thunderbird interface
It adds some icons and main menu items to Thunderbird. To actually work in ReminderFox, an icon or Tools menu selection opens ReminderFox in a separate window rather than as a tab within Thunderbird. You would use that if you want to use ReminderFox features beyond simple email reminders.
Within the Thunderbird email panel, you can identify messages with reminders by making Tag one of the displayed fields from the customization (select columns to display) icon. An icon can also be added to Thunderbird's menu bar to give you quick access to upcoming notifications.
For users of other email clients, this article may be useful in identifying a similar solution. It's a blog written by the makers of Boomerang for Gmail, but it covers a wide range of products and is well done.
Update: The ReminderFox developers decided not to invest in rewriting the software to support Mozilla's change to Firefox with Quantum. They closed their website and moved to Github; I've updated the developer links in this answer. It is still supported for Thunderbird through the version 60 series, and available as an add-on. However, they have announced they are throwing in the towel and won't be supporting v65 and beyond (see https://groups.google.com/forum/#!msg/reminderfox/MlYIeFOtpMs/0RiFOQbuAwAJ). I can't guarantee that the detail shown is this answer is still accurate for the version currently available.