and what format are your contact stored in? A Dat file is a completely non application and non format specific file format.

I did a google search and that indicates that em client stores contact in a custom SQLITE database. It also indicates that em client can export contact to both CSV and VCF (Vcard) formats. Thunderbird can import both of those formats. So it is over to you to get you EM client data into a usable format.

Thanks for replying Matt. As I pointed out in my request for help, I have all the DATA files stored on my pen drive, but since eM Client has moved from ver9 to ver 10, it will not read my DATA files, which are in ver 9 form. Even 30 pages of help from Chat GPT did not give a solution, because eM Client will not allow me to download a workable ver 9 or 10. I have wasted 2 months of Chat GPT's and my time trying to fix what Chat GPT calls eM Client's "brittle" data storage system. I could spend approx. $300 to rent a program to extract and restore my data, so that it could be read by Thunderbird. I'm 81, on a small pension and cannot afford to get "eM Client data into a usable format". Plus, it should be up to eM Client to make its data files transferable, when it crashes.

Anyway, more importantly, Thunderbird has decided to hide all the new "Local folders" that I so carefully set up last night. I right clicked on "Local folders", then on "new folder" to set up each of my storage folders for "fishing club" "boat", "friends" etc and filled each one with the applicable email. I then opened each labled folder, to check that I had done things correctly. Each opened perfectly. Closed down Thunderbird last night, but on opening TB tonight all 12 "Local folders" have disappeared.

I use an SSD for working and a HDD for all my data, music, photos. One bit of good news is, somehow most of my contacts have been imported from my C: drive to my E: drive, but, as with my local folders, TB has also hidden them. Forget about the loss of 10 years of emails and my large "contacts" folder, can you just help me "show hidden folders" in TB please

Version 9 can be downloaded here, in case you need to read the DAT files:

https://www.emclient.com/release-history?os=win

eM Client exports mail to eml files, which can be imported to TB: create a subfolder of Local Folders, then add eml files by drag and drop from Windows Explorer.

Many thanks sfhowes, for trying to help. I followed your instructions, found the web page, downloaded the program that I've used successfully a number of times before and hit "install". Unlike the many installs before, this one took 3 mins and eventually told me that it had failed to install. This just confirmed that whatever I do, I will never restore all my emails etc. Chat GPT said it was a lost cause, because eM Client has a "brittle" data recovery system and I have accepted that, although I would have used a different description of its "recovery system", After 2 months of working on this problem, I have decided that life is too short (at least for me, at 81) to use up valuable time on a failed cause. Let's forget about eM Client (its very name now causes me grief) and concentrate on trying to stop TB from following its example. All I want is for TB to give me back my " Local Folders" (please refer to my previous post). A hint or two on importing my "contacts" folder, would also cheer me up. Please help.