Ignoring the letter is the only guaranteed way to get into trouble. In most states, the court doesn't send a sheriff after a first-time no-show, but they will issue a bench warrant or an Order to Show Cause. You do not want to explain to a judge why you threw the card in the recycling bin.
“I request to postpone my service from March 15th to September 5th.” postpone jury duty better
Here is the loophole: When you postpone, request “standby service.” This means you call a phone number each night for a week. If your number isn’t called, you are done. Ignoring the letter is the only guaranteed way