I'm not a user of Copernic, but it appears the TB extension can be purchased for US$30 per year:

https://copernic.com/en/desktop/pricing/

Not sure if they offer a trial version.

I too have this problem after the last Copernic update. The use of the word "extension" is somewhat confusing.

When buying a version of Copernic, it comes with a variety of Copernic extensions or utilities, depending on the price. In my case, I have the basic Copernic plus licensed Copernic extensions for indexing/searching email, MS file types etc. I attach a shot of that bit of it.

However, since the new Copernic release, the message as per screenshot appears. This is definitely a reference to a Thunderbird add-on in "Add ons and Themes". See screenshot referring to this.

I will get back to Copernic to see if I can get an answer.

I've been having another look at this while I wait for Copernic's answer.

I'm able to index Tbird emails if I do these things:- 1) Ensure that the Tbird profile folder is set in the Copernic Tools>Files setting 2) Ensure that the .eml file type is also set up in Tools>Advanced 3) In the Copernic Extensions/Licences window, make sure that the Thunderbird extension has the "Use Legacy Plugin" box checked.

You should find that without that box checked, the error message about the Connector will appear. Check it, and the error should not appear.

I'd be interested to know how you get on.

I am sure that I carefully looked through all my TB addons yesterday, but today I notice that there is the Copernic Connector in the disabled section. This has the attribute of "can't be removed" and doesn't seem to appear in any source of update information. I think that it must have arrived direct from Copernic with the latest Copernic update, and not from the Add-ons store.

I'll see if this does the job.

@MsLuctoretemergo I have now had a complete and rapid answer from Copernic, and, with their permission, am able to post their response below. Quote " After installation of Copernic 8.3.3, restart Thunderbird and you will see a new Copernic add-on (yellow icon). Please enable this extension in Thunderbird and you will now be able to use the new Thunderbird extension with all the improvements.

If this does not show, you can enable the extension under the hamburger button > Add-ons and themes. Click on the gear icon and select "Install an Add-on from a file..." then select the file "ThunderbirdConnector.xpi" from this folder: "C:\Program Files\Copernic\DesktopSearch\ThunderbirdConnector"

Also make sure the "Use Legacy Plugin" option is NOT checked in Extensions / Licenses in Copernic."

I think this answers it all.