You have a few options when you receive a cease and desist letter from an old employer. You can
1. Use the letter to line your guinea pig’s cage.
2. Ignore the letter but keep it.
3. Respond to the letter informally – “Hey, got your letter” at which point you stick out your tongue, put your fingers in your ears and split making the “Pltth. sound.”
4. Respond to the letter formally, by sending a letter that says “Hey got your letter… bring it.”
5. Have an attorney review your contract, discuss which option is best as well as your ability to litigate should suit be filed, and respond according to your situation and needs.
You have many choices – some of which are fun, one of which will help you in the long run.