I've had a hunt around and there is an addon called mailmindr: https://addons.thunderbird.net/en-GB/thunderbird/addon/mailmindr/

Please note that addon extensions are the responsibility of the author and not Thunderbird. So authors respectfully ask people who use their addon to make a donation to help them continue with maintenance of the addon. The developer of this add-on asks that you help support its continued development by making a small contribution.

Also Snoozing is something you can do for events or Tasks in Calendar. Emails can be converted to Events or Tasks using right click on email in list 'Convert to' > 'Task' Where you can choose time and reminder. There is an addon which can offer more snooze options in calendar (used to be called Lightning) https://addons.thunderbird.net/en-us/thunderbird/addon/more-snooze/

How to install an addon: https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

Thanks for your reply. mailmindr does the job perfectly, thank you.

Thanks also for the hint about creating events and tasks. I've added Provider for Google Calendar and experimenting with that.

You can use right click on email and select 'Convert to' > 'Event' and select the google or Home calendar. You can also locate this convert to option via the 'More' icon located far right in the header area of an opened email.

'Convert to' > 'Tasks' only offers the Home option.

Google keep the Tasks as a separate listed calendar. However, there is a way.... To use 'Convert to' > 'Tasks' and use google - you need to : Logon to your google Calendar via a browser and under 'My Calendars' select 'Tasks' so it is enabled. (you probably have this already selected)

In Thunderbird, you now need to add a 'New calendar' File > New > Calendar select 'Google Calendar' and click on 'Next' Your gmail address should already be showing - select it and click on 'Find Calendar' You should see a list of Calendars and also 'Tasks List' - select 'My Tasks' and click on 'Subscribe' Select 'Calendar' tab 'My Tasks' will now appear in the 'Calendar' list.

Now when you right click on email and choose 'Convert to' > 'Task', whilst the default 'Home' calendar is auto selected, you should be able to use the drop down to select 'My Tasks'

I have just tested this and used 'Convert to' > 'Task' > choose 'MyTasks' and saved it. Logged into Google to see Calendar and checked the task list and it was there.

Note: I've added Provider for Google Calendar and experimenting with that. The latest version of Thunderbird now has built in ability to connect to Google calendar and so does not need to use an addon, but the addon does work perfectly ok.

I couldn't get Calendar and tasks to work correctly before installing Provider for Google Calendar but since installing it seems to work fine.

Toad-Hall, just wanted to mention as I have experimented with creating tasks further, that convert to Google tasks works much better for me than snoozing emails.

I work on both a desktop and laptop, google tasks synchronises across all my devices whereas snoozing doesn't.

Thanks again for your very helpful advice.