inadvertently how?

I was cLeaning out obsolete files and came accross a listing of Taxation Clients with no addresses and deleted it not realising that it contained all the emails Chris

I am getting more, not less confused. If you delete something in Thunderbird it goes to the trash folder.

If you delete files in your operating system is does much the same thing. There are ways to circumvent those protections. Like holding shift while you do it, but really if you did that then the information is gone. if it is in the trash move it out of the trash.