diff --git a/tests/dGameTests/CMakeLists.txt b/tests/dGameTests/CMakeLists.txt
index 145726161..33deaa1a9 100644
--- a/tests/dGameTests/CMakeLists.txt
+++ b/tests/dGameTests/CMakeLists.txt
@@ -3,6 +3,7 @@ set(DGAMETEST_SOURCES
 	"GuildManagerTests.cpp"
 	"LUBitStreamTests.cpp"
 	"MailIdPinTests.cpp"
+	"MailPacketTests.cpp"
 	"EconomyLedgerTests.cpp"
 	"PlayerReportsLimitTests.cpp"
 	"SlashCommandPermissionTests.cpp"
diff --git a/tests/dGameTests/MailPacketTests.cpp b/tests/dGameTests/MailPacketTests.cpp
new file mode 100644
index 000000000..199754576
--- /dev/null
+++ b/tests/dGameTests/MailPacketTests.cpp
@@ -0,0 +1,183 @@
+// Pins the bytes of the mail packets and the mailbox messages against the layout the client reads for the mail
+// list and notifications, and against live captures. Padding in the captures holds uninitialized memory; the
+// expected bytes below use zero there, which is what DLU writes and what the client ignores.
+
+#include "Mail.h"
+#include "MailInfo.h"
+#include "EffectsMessages.h"
+#include "ObjectMessages.h"
+#include "Amf3.h"
+#include "PacketTestUtils.h"
+
+#include <cstring>
+#include <string>
+
+#include <gtest/gtest.h>
+
+using PacketTestUtils::FromBitStream;
+using PacketTestUtils::FromHex;
+using PacketTestUtils::PacketsEqual;
+
+namespace {
+	// Little endian writer for building the expected bytes field by field.
+	struct Bytes {
+		std::vector<uint8_t> data;
+		template<typename T> void Put(const T value) {
+			uint8_t raw[sizeof(T)];
+			std::memcpy(raw, &value, sizeof(T));
+			data.insert(data.end(), raw, raw + sizeof(T));
+		}
+		// Fixed size UTF-16 field, zero filled
+		void PutWide(const std::string& text, const size_t chars) {
+			for (size_t i = 0; i < chars; i++) Put<uint16_t>(i < text.size() ? static_cast<uint16_t>(text[i]) : 0);
+		}
+		PacketTestUtils::PacketBytes Packet() const { return { data, static_cast<uint32_t>(data.size() * 8) }; }
+	};
+
+	void PutClientMailHeader(Bytes& b, const Mail::eMessageID id) {
+		b.Put<uint8_t>(0x53);     // ID_USER_PACKET_ENUM
+		b.Put<uint16_t>(5);       // ServiceType::CLIENT
+		b.Put<uint32_t>(0x31);    // MessageType::Client::MAIL
+		b.Put<uint8_t>(0);
+		b.Put<uint32_t>(static_cast<uint32_t>(id));
+	}
+
+	PacketTestUtils::PacketBytes Write(const LUBitStream& packet) {
+		RakNet::BitStream bitStream;
+		packet.WritePacket(bitStream);
+		return FromBitStream(bitStream);
+	}
+
+	PacketTestUtils::PacketBytes Write(const GameMessages::NetGameMsg& msg) {
+		RakNet::BitStream bitStream;
+		msg.WritePacket(bitStream);
+		return FromBitStream(bitStream);
+	}
+}
+
+// An empty mailbox: throttled 0, count 0. The client clears its list and sends LoadMailList with no entries.
+TEST(MailPacketTests, EmptyDataResponse) {
+	Mail::DataResponse response;
+	Bytes expected;
+	PutClientMailHeader(expected, Mail::eMessageID::DataResponse);
+	expected.Put<uint32_t>(0); // throttled
+	expected.Put<uint16_t>(0); // count
+	expected.Put<uint16_t>(0); // padding
+	ASSERT_EQ(expected.data.size(), 20u);
+	EXPECT_TRUE(PacketsEqual(expected.Packet(), Write(response)));
+}
+
+// One player mail with an attachment, values from a live capture (100 of LOT 3038 from another player).
+// Every entry is 1040 bytes.
+TEST(MailPacketTests, DataResponseEntryMatchesLive) {
+	MailInfo mail;
+	mail.id = 0x100000016c4b30e2;
+	mail.subject = "blue1";
+	mail.body = "";
+	mail.senderUsername = "ShastaFantastic";
+	mail.itemID = 0x100000016c4b30e3;
+	mail.itemLOT = 3038;
+	mail.itemSubkey = 0;
+	mail.itemCount = 100;
+	mail.timeSent = 1327102410;
+	mail.wasRead = false;
+
+	Mail::DataResponse response;
+	response.playerMail.push_back(mail);
+
+	Bytes expected;
+	PutClientMailHeader(expected, Mail::eMessageID::DataResponse);
+	expected.Put<uint32_t>(0); // throttled
+	expected.Put<uint16_t>(1); // count
+	expected.Put<uint16_t>(0);
+	const auto entryStart = expected.data.size();
+	expected.Put<uint64_t>(0x100000016c4b30e2); // mail id
+	expected.PutWide("blue1", 50);               // subject
+	expected.PutWide("", 400);                   // body
+	expected.PutWide("ShastaFantastic", 32);     // sender
+	expected.Put<uint32_t>(0);
+	expected.Put<uint64_t>(0);                   // attached currency
+	expected.Put<int64_t>(0x100000016c4b30e3);   // attachment object id
+	expected.Put<int32_t>(3038);                 // attachment LOT
+	expected.Put<uint32_t>(0);
+	expected.Put<int64_t>(0);                    // attachment subkey
+	expected.Put<int16_t>(100);                  // attachment count
+	expected.Put<uint8_t>(0);                    // subject type
+	expected.Put<uint8_t>(0);
+	expected.Put<uint32_t>(0);
+	expected.Put<uint64_t>(1327102410);          // expiration
+	expected.Put<uint64_t>(1327102410);          // sent
+	expected.Put<uint8_t>(0);                    // was read
+	expected.Put<uint8_t>(0);                    // is localized (player mail)
+	expected.Put<uint16_t>(1033);                // language
+	expected.Put<uint32_t>(0);
+	ASSERT_EQ(expected.data.size() - entryStart, 1040u);
+
+	EXPECT_TRUE(PacketsEqual(expected.Packet(), Write(response)));
+}
+
+// No attachment: the client checks for LOT -1 (LOT_NULL), not 0.
+TEST(MailPacketTests, NoAttachmentIsLotNull) {
+	MailInfo mail;
+	mail.itemLOT = 0;
+	RakNet::BitStream bitStream;
+	mail.Serialize(bitStream);
+	const auto bytes = FromBitStream(bitStream).bytes;
+	ASSERT_EQ(bytes.size(), 1040u);
+	int32_t lot{};
+	std::memcpy(&lot, bytes.data() + 8 + 100 + 800 + 64 + 4 + 8 + 8, sizeof(lot));
+	EXPECT_EQ(lot, -1);
+}
+
+// Answer to NotificationRequest: 56 bytes, the unread count at offset 48 (live sent 2 there for two unread mails).
+TEST(MailPacketTests, NotificationResponseLayout) {
+	Mail::NotificationResponse response;
+	response.status = Mail::eNotificationResponse::NewMail;
+	response.mailCount = 2;
+	const auto actual = Write(response);
+	ASSERT_EQ(actual.bytes.size(), 56u);
+	Bytes expected;
+	PutClientMailHeader(expected, Mail::eMessageID::NotificationResponse);
+	expected.Put<uint32_t>(0); // NewMail
+	expected.Put<uint64_t>(0);
+	expected.Put<uint64_t>(0);
+	expected.Put<uint64_t>(0);
+	expected.Put<uint64_t>(0);
+	expected.Put<uint32_t>(2); // mail count
+	expected.Put<uint32_t>(0);
+	EXPECT_TRUE(PacketsEqual(expected.Packet(), actual));
+}
+
+// The mailbox opens the Mail UI with pushGameState {state: "Mail"}; bytes from a live capture.
+TEST(MailPacketTests, MailboxPushGameStateMatchesLive) {
+	GameMessages::UIMessageServerToSingleClient msg;
+	msg.target = 0x100000015b7b141f;
+	msg.strMessageName = "pushGameState";
+	msg.args.Insert("state", "Mail");
+	EXPECT_TRUE(PacketsEqual(
+		FromHex("5305000c000000001f147b5b01000010a00409010b737461746506094d61696c010d0000007075736847616d655374617465"),
+		Write(msg)));
+}
+
+// Closing the mailbox: ToggleMail {visible: false}; bytes from a live capture.
+TEST(MailPacketTests, MailboxToggleMailMatchesLive) {
+	GameMessages::UIMessageServerToSingleClient msg;
+	msg.target = 0x100000015b7b141f;
+	msg.strMessageName = "ToggleMail";
+	msg.args.Insert("visible", false);
+	EXPECT_TRUE(PacketsEqual(
+		FromHex("5305000c000000001f147b5b01000010a00409010f76697369626c6502010a000000546f67676c654d61696c"),
+		Write(msg)));
+}
+
+// After pushGameState the mailbox itself is told OpenMail, and CloseMail after ToggleMail; its client script keeps
+// the mailbox marked in use (no interact icon, no second use) in between. Bytes from a live capture.
+TEST(MailPacketTests, MailboxOpenCloseNotifyMatchesLive) {
+	constexpr LWOOBJID mailbox = 0x000044800000b5c0;
+	EXPECT_TRUE(PacketsEqual(
+		FromHex("5305000c00000000c0b50000804400001204080000004f00700065006e004d00610069006c000000000000000000000000000000000000000000"),
+		Write(GameMessages::NotifyClientObject(mailbox, u"OpenMail"))));
+	EXPECT_TRUE(PacketsEqual(
+		FromHex("5305000c00000000c0b500008044000012040900000043006c006f00730065004d00610069006c000000000000000000000000000000000000000000"),
+		Write(GameMessages::NotifyClientObject(mailbox, u"CloseMail"))));
+}