Как сравнить и выбрать DNS сервер?

А mail.ru у вас открывается напрямую или через варп? Можно посмотреть в логе sing-box, напрямую будет outbound/direct[direct]: outbound connection to mail.ru:443 Если через варп, то endpoint/wireguard[warp]: outbound connection to mail.ru:443
Проверьте маршрутизацию, должно быть примерно так

Пример рабочего конфига sing-box_extended_v1.13 (вместо *** нужно подставить свои значения)
{
	"certificate": {
		"store": "system"
	},
	"dns": {
		"servers": [
			{
				"detour": "warp",
				"tag": "doh-remote",
				"type": "https",
				"server": "9.9.9.9",
				"path": "dns-query",
				"tls":
				{
					"server_name": "dns.quad9.net"
				}
			},		
			{
				"tag": "doh-local",
				"type": "https",	
				"server": "77.88.8.8",
				"path": "dns-query",
				"tls":
				{
					"server_name": "common.dot.dns.yandex.net"
				}
			},
			{
				"detour": "warp",
				"tag": "dns-remote",
				"type": "udp",		
				"server": "9.9.9.9"
			},
			{
				"tag": "dns-local",
				"type": "local"
			}	
		],
		"disable_cache": false,
		"final": "doh-remote",
		"rules": 
		[
			{
				"server": "doh-local",					
				"rule_set": [
					"geoip-ru",
					"geosite-ru",
					"geosite-category-ru",
					"geosite-ru-available-only-inside"
				],
				"action": "route",
				"strategy": "ipv4_only"
			},			
			{
				"server": "doh-remote",
				"action": "route",
				"strategy": "prefer_ipv6"
			}
		]
	},
	"log": {
		"level": "info",
		"timestamp": true,
		"output": "Warp.log"
	},
	"inbounds": [
		{
			"tag": "in",
			"listen": "127.0.0.1",
			"listen_port": 1080,
			"type": "mixed"
		}
	],
	"outbounds": [
		{
			"tag": "direct",
			"type": "direct"
		}		
	],
	"endpoints": [
		{
			"tag": "warp",
			"type": "wireguard",
			"peers": [
				{
					"address": "162.159.195.1",
					"port": 1701,
					"public_key": "bmXOC+F1FxEMF9dyiK2H5/1SUtzH0JuVo51h2wPfgyo=",
					"allowed_ips": ["0.0.0.0/0", "::/0"],
					"persistent_keepalive_interval": 15
				}
			],
			"private_key": "***",
			"address": ["172.16.0.2/32", "***"],
			"mtu": 1280,
			"amnezia": {
				"jc": 0,
				"jmin": 0,
				"jmax": 0,
				"s1": 0,
				"s2": 0,
				"s3": 0,
				"s4": 0,
				"h1": 1,
				"h2": 2,
				"h3": 3,
				"h4": 4,
				"i1": "***",
				"i2": "",
				"i3": "",
				"i4": "",
				"i5": "",
				"j1": "",
				"j2": "",
				"j3": "",
				"itime": 0
			}
		}
	],
	"route": {
		"find_process": true,
		"final": "warp",
		"default_domain_resolver": {
			"server": "doh-remote",
			"strategy": ""
		},
		"rule_set": [
			{
				"format": "binary",
				"tag": "geoip-ru",
				"type": "remote",
				"url": "https://testingcf.jsdelivr.net/gh/MetaCubeX/meta-rules-dat@sing/geo/geoip/ru.srs"
			},
			{
				"format": "binary",
				"tag": "geosite-ru",
				"type": "remote",
				"url": "https://testingcf.jsdelivr.net/gh/hiddify/hiddify-geo@rule-set/country/geosite-ru.srs"
			},
			{
				"format": "binary",
				"tag": "geosite-category-ru",
				"type": "remote",
				"url": "https://testingcf.jsdelivr.net/gh/MetaCubeX/meta-rules-dat@sing/geo/geosite/category-ru.srs"
			},
			{
				"format": "binary",
				"tag": "geosite-ru-available-only-inside",
				"type": "remote",
				"url": "https://testingcf.jsdelivr.net/gh/runetfreedom/russia-v2ray-rules-dat@release/sing-box/rule-set-geosite/geosite-ru-available-only-inside.srs"
			}
		],
		"rules": [
			{
				"action": "route",
				"outbound": "direct",
				"rule_set": [
					"geoip-ru",
					"geosite-ru",
					"geosite-category-ru",
					"geosite-ru-available-only-inside"
				]
			},
			{
				"inbound": "in",
				"action": "resolve"				
			}			
		]		
	}
}

В общем разобрался. Проблема оказалась если на wan порту раутера нет ipv6, то “strategy”: “prefer_ipv4” не работает, только ipv4_only.