I encourage all persons running a business to do backups regularly, as software and hardware sometimes have glitches. (In fact, I encourage everyone who creates important content on a computer, such as email, to make regular backups. If they did, there would be little need for this forum.) Although your business problems are unfortunate, Thunderbird cannot be responsible. Since you have already been deleting files, it may be difficult to reconstruct your issues, but if you will give more information, plus any error messages, someone here may have suggestions.