Bring a large pot of water to a boil. Meanwhile, prepare an ice-water bath. Cut a small x in the bottom of each peach. Boil peaches for 1 minute.*
Transfer to ice-water bath. Let cool slightly. Peel and pit peaches, and cut into 3/4-inch-thick wedges.
Bring 4 cups of water, the sugar, vanilla seeds and pods, and lemon zest strips to a boil in a large saucepan, stirring until sugar dissolves. Add peaches and rum. Simmer until peaches are tender but still hold their shape, 5 to 7 minutes.
Transfer peaches to a large bowl using a slotted spoon. Cook syrup over medium heat and reduce syrup by half, about 15 minutes. Taste the syrup and add lemon juice to taste. Pour over peaches. Let cool completely. Store in a glass container unless you want to can them. If you do, read on. If you don’t, store the vanilla beans with the peaches. When you’ve used up the peaches, rinse the vanilla beans, pat dry, and store in your sugar or reuse one more time in cooking.
Divide peaches among five 12-ounce sterilized jars using a slotted spoon. Pour syrup over tops and add pieces of the vanilla pods to the jars. Seal jars and refrigerate until ready to use, or process. If you want to process them, check online or in a cookbook for instructions.
*I skipped this step as the peaches peeled easily enough, but if yours don’t or you hate peeling peaches, it’s a good tip.