Also add that I can no longer receive emails either. I get the notification that new email is available to download, but when Thunderbird begins to download the new messages, I get the following error message:

Unable to write the email to the mailbox. Make sure the file system allows you write privileges, and you have enough disk space to copy the mailbox.

I've checked the affected files, and still have CRUD privileges to all of them.

What is your anti-virus software?

Good point, hadn't thought of that. McAfee.

Try to create an exception in your anti-virus software for the Thunderbird profile folder, so that the anti-virus real-time scanner will not scan it. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_how-to-find-your-profile

McAfee has been problematic in connection with Thunderbird in the past, and I doubt that this has changed for the better by now. Therefore you may want to get rid of McAfee altogether, and just stick with Microsoft Defender.

I've excluded the Inbox, Inbox.msf, Trash and Trash.msf files in McAfee AV scanning. However, the damage may have already been done as, per my expectations, I still get the same error messages.

Hello there

Most of the issue that are been caused just like this problem on that pc with Thunderbird version s is mostly caused by antivirus software that is to strong for that little system to scan or is interrupted by a lot of vpn options and scans like described above .

It seems to be that a lot of point s can direct to that issue.Network congestion.Or profiles that are connected and can synchronize to the cloud with a location there by to stream to it or having backup s over there in the cloud .

Having one of this futures try to configure them by turning it off or delete them.putting them back as a option to it.

Try to start Windows 10 in safe mode with networking enabled.

Still in Windows safe mode, start Thunderbird in safe mode. Does the problem go away?

Windows safe mode disables anti-virus software. This is a troubleshooting step, not a solution.

Hello there

If you only have that issue of having trouble by deleting that message or more It might be the trashcan that is corrupted or damaged and had to be scanned or replaced .

So I solved the problem by uninstalling Thunderbird 115.10.1 and reinstalling 115.09.01 and copying all my emails into the new profile structure under the AppInfo > Thunderbird folder. Thanks everyone for your help, apologies that none of the suggestions worked as I know how it feels to offer out of kindness and not get a resolution.

Cheers! Loc