using System.Collections.Generic;
public static void Main()
var templateValueList = new List<string> { "some", "long", "template", "values" };
var body = "some long template string. {{0}} {{1}} {{2}} {{3}}";
for (var i = 0; i < templateValueList.Count; i++) {
body = body.Replace("{{" + i + "}}", templateValueList[i]);