diff --git a/hwe/sammo/Message.php b/hwe/sammo/Message.php
index 1a140d4f..aca0c872 100644
--- a/hwe/sammo/Message.php
+++ b/hwe/sammo/Message.php
@@ -15,6 +15,9 @@ class Message
 
     protected $sendCnt = 0;
 
+    private ?int $sendTimeTick = null;
+    private ?int $sendValidUntilTick = null;
+
     public function __construct(
         public MessageType $msgType,
         public MessageTarget $src,
@@ -324,15 +327,7 @@ class Message
 
         $db = DB::db();
         $clock = GameClock::fromStorage(KVStorage::getStorage($db, 'game_env'));
-        $timeTick = $clock->nowTick();
-        if (Util::toInt($this->validUntil->format('Y')) >= 9000) {
-            $validUntilTick = GameClock::MAX_SAFE_TICK;
-        } else {
-            $validitySeconds = $this->validUntil->getTimestamp() - $this->date->getTimestamp();
-            $validUntilTick = $timeTick + $clock->ticksFromSeconds($validitySeconds);
-        }
-        $this->date = \DateTime::createFromImmutable($clock->tickToDateTime($timeTick));
-        $this->validUntil = \DateTime::createFromImmutable($clock->tickToDateTime($validUntilTick));
+        [$timeTick, $validUntilTick] = $this->resolveSendTicks($clock);
         $db->insert('message', [
             'mailbox' => $mailbox,
             'type' => $this->msgType->value,
@@ -350,6 +345,32 @@ class Message
         return [$mailbox, $db->insertId()];
     }
 
+    /** @return array{0:int, 1:int} */
+    protected function resolveSendTicks(GameClock $clock): array
+    {
+        if ($this->sendTimeTick !== null && $this->sendValidUntilTick !== null) {
+            return [$this->sendTimeTick, $this->sendValidUntilTick];
+        }
+
+        $timeTick = $clock->nowTick();
+        if (Util::toInt($this->validUntil->format('Y')) >= 9000) {
+            $validUntilTick = GameClock::MAX_SAFE_TICK;
+        } else {
+            $validitySeconds = $this->validUntil->getTimestamp() - $this->date->getTimestamp();
+            $validUntilTick = GameClock::addTicks(
+                $timeTick,
+                $clock->ticksFromSeconds($validitySeconds),
+            );
+        }
+
+        $this->sendTimeTick = $timeTick;
+        $this->sendValidUntilTick = $validUntilTick;
+        $this->date = \DateTime::createFromImmutable($clock->tickToDateTime($timeTick));
+        $this->validUntil = \DateTime::createFromImmutable($clock->tickToDateTime($validUntilTick));
+
+        return [$timeTick, $validUntilTick];
+    }
+
     private function sendToSender():array{
         if($this->sendCnt > 1){
             throw new \RuntimeException('이미 전송한 메일입니다.');
diff --git a/tests/MessageGameClockTest.php b/tests/MessageGameClockTest.php
new file mode 100644
index 00000000..96f3c064
--- /dev/null
+++ b/tests/MessageGameClockTest.php
@@ -0,0 +1,95 @@
+<?php
+
+namespace sammo;
+
+use PHPUnit\Framework\TestCase;
+use sammo\Enums\MessageType;
+
+require_once __DIR__ . '/../hwe/sammo/Target.php';
+require_once __DIR__ . '/../hwe/sammo/MessageTarget.php';
+require_once __DIR__ . '/../hwe/sammo/Enums/MessageType.php';
+require_once __DIR__ . '/../hwe/sammo/Message.php';
+
+final class MessageGameClockTest extends TestCase
+{
+    public function testUnlimitedMessageReusesExactTicksAcrossReceiverAndSenderCopies(): void
+    {
+        $base = new \DateTimeImmutable('2026-08-04 00:00:00.000000');
+        $wallTimes = [
+            new \DateTimeImmutable('2026-08-04 00:00:00.000000'),
+            new \DateTimeImmutable('2026-08-04 00:00:00.938140'),
+        ];
+        $wallReads = 0;
+        $clock = new GameClock(
+            $base,
+            1,
+            0,
+            GameClock::MODE_REALTIME,
+            $base,
+            static function () use (&$wallTimes, &$wallReads): \DateTimeImmutable {
+                return $wallTimes[$wallReads++];
+            },
+        );
+        $message = new TestableClockMessage(
+            MessageType::national,
+            $this->createMock(MessageTarget::class),
+            $this->createMock(MessageTarget::class),
+            '선전포고',
+            new \DateTime('2026-08-04 00:00:00.000000'),
+            new \DateTime('9999-12-31'),
+            [],
+        );
+
+        $receiverTicks = $message->resolveTicksForTest($clock);
+        self::assertLessThan(9000, Util::toInt($message->validUntil->format('Y')));
+        $legacySecondClock = new GameClock(
+            $base,
+            1,
+            0,
+            GameClock::MODE_REALTIME,
+            $base,
+            static fn (): \DateTimeImmutable => $wallTimes[1],
+        );
+        $legacySecondNowTick = $legacySecondClock->nowTick();
+        self::assertSame(562_884, $legacySecondNowTick);
+        $legacySecondExpiry = $legacySecondNowTick + $clock->ticksFromSeconds(
+            $message->validUntil->getTimestamp() - $message->date->getTimestamp(),
+        );
+        self::assertSame(9_007_199_254_762_884, $legacySecondExpiry);
+        $senderTicks = $message->resolveTicksForTest($clock);
+
+        self::assertSame([0, GameClock::MAX_SAFE_TICK], $receiverTicks);
+        self::assertSame($receiverTicks, $senderTicks);
+        self::assertSame(1, $wallReads);
+    }
+
+    public function testFiniteMessageCachesOneValidatedExpiryForBothCopies(): void
+    {
+        $base = new \DateTimeImmutable('2026-08-04 00:00:00.000000');
+        $clock = new GameClock($base, 1, 120_000, GameClock::MODE_MANUAL, $base);
+        $message = new TestableClockMessage(
+            MessageType::national,
+            $this->createMock(MessageTarget::class),
+            $this->createMock(MessageTarget::class),
+            '유한 메시지',
+            new \DateTime('2026-08-04 00:00:02.000000'),
+            new \DateTime('2026-08-04 00:01:02.000000'),
+            [],
+        );
+
+        $receiverTicks = $message->resolveTicksForTest($clock);
+        $senderTicks = $message->resolveTicksForTest($clock);
+
+        self::assertSame([120_000, 36_120_000], $receiverTicks);
+        self::assertSame($receiverTicks, $senderTicks);
+    }
+}
+
+final class TestableClockMessage extends Message
+{
+    /** @return array{0:int, 1:int} */
+    public function resolveTicksForTest(GameClock $clock): array
+    {
+        return $this->resolveSendTicks($clock);
+    }
+}