My former employer is threatening me with a lawsuit for; 1) stealing their customer list and marketing to them, and 2) stealing their software and IP.
Neither of these are true, and I am not responding to their shakedown letter.
Would anybody like to offer sage advice, anecdotes, or pro bono advice to cheer me up?
My layman opinion is that he will have to prove his claims, and is probably trying to scare you into giving him your client list.
I understand how ridiculous the threat might feel. But a sufficiently angry person can cause you a lot of trouble for no good reason. It's very likely there are simple actions you could take safeguard yourself. It might save you a lot of money in the long term. And very often even the major law firms will give you amazing free advice. Don't be afraid to call the best.
[0] And I mean relate in the broadest manner. It doesn't have to actually be related. If they could convince someone with a bit of handwaving that it's related then it's related. The truth doesn't matter.
If neither of these are true, and you are in fact marketing to customers but not using their list or software, gather logs and customer testimonials, and proof about where you got the customer contacts.
Additionally, gather emails indicating why you left the company or were asked to leave, as it might indicate the company's intent to get even with you.
Lastly, talk to a lawyer. Consultation is often free for the first time.
Making public statements that disparage the company could expose him to a libel suit (whether justified or not), which could add more to his legal expenses than he can afford to pay.
This is awful advice.