diff --git a/src/repositories/letter.repository.js b/src/repositories/letter.repository.js
index c695160..249ae6a 100644
--- a/src/repositories/letter.repository.js
+++ b/src/repositories/letter.repository.js
@@ -467,4 +467,112 @@ export const selectQueuedLetter = async () => {
     })
 
     return letter;
-}
\ No newline at end of file
+}
+
+// 세션별 편지 개수 조회
+export const countLettersBySessionIdAndUserId = async ({ sessionId, userId, letterType }) => {
+  return await prisma.letter.count({
+    where: {
+      letterType,
+      sessionId: sessionId,
+      OR: [
+        { receiverUserId: userId },
+        { senderUserId: userId }
+      ]
+    }
+  });
+};
+
+// 세션별 읽지 않은 편지 개수 조회
+export const countUnreadLettersBySessionIdAndUserId = async ({ sessionId, userId, letterType }) => {
+  return await prisma.letter.count({
+    where: {
+      letterType,
+      sessionId: sessionId,
+      receiverUserId: userId,
+      readAt: null,
+    }
+  });
+};
+
+// 세션별 받은 편지 조회
+export const findReceivedLettersBySessionIdAndUserId = async ({ sessionId, userId, letterType }) => {
+  return await prisma.letter.findMany({
+    where: {
+      receiverUserId: userId,
+      sessionId: sessionId,
+      letterType,
+    },
+    orderBy: [{ deliveredAt: "desc" }, { createdAt: "desc" }],
+    select: {
+      id: true,
+      title: true,
+      deliveredAt: true,
+      readAt: true,
+      createdAt: true,
+      question: {
+        select: {
+          content: true
+        }
+      },
+      design: {
+        select: {
+          paper: {
+            select: {
+              id: true,
+              color: true,
+            }
+          },
+          stamp: {
+            select: {
+              id: true,
+              name: true,
+              assetUrl: true
+            }
+          },
+        },
+      },
+    },
+  });
+};
+
+// 세션별 보낸 편지 조회
+export const findSentLettersBySessionIdAndUserId = async ({ sessionId, userId, letterType }) => {
+  return await prisma.letter.findMany({
+    where: {
+      senderUserId: userId,
+      sessionId: sessionId,
+      letterType,
+    },
+    orderBy: [{ deliveredAt: "desc" }, { createdAt: "desc" }],
+    select: {
+      id: true,
+      title: true,
+      deliveredAt: true,
+      readAt: true,
+      createdAt: true,
+      question: {
+        select: {
+          content: true
+        }
+      },
+      design: {
+        select: {
+          paper: {
+            select: {
+              id: true,
+              color: true,
+            }
+          },
+          stamp: {
+            select: {
+              id: true,
+              name: true,
+              assetUrl: true
+            }
+          },
+        },
+      },
+    },
+  });
+};
\ No newline at end of file
diff --git a/src/repositories/session.repository.js b/src/repositories/session.repository.js
index 86af207..01ef6f5 100644
--- a/src/repositories/session.repository.js
+++ b/src/repositories/session.repository.js
@@ -202,3 +202,24 @@ export const countMatchingSessionByUserId = async (userId) => {
 
   return count;
 };
+
+// 세션 ID와 사용자 ID로 세션 조회 (참가자 포함)
+export const findMatchingSessionBySessionIdAndUserId = async ({ sessionId, userId }) => {
+  return await prisma.matchingSession.findFirst({
+    where: {
+      id: sessionId,
+      participants: {
+        some: {
+          userId: userId
+        }
+      }
+    },
+    include: {
+      participants: {
+        select: {
+          userId: true
+        }
+      }
+    }
+  });
+};
\ No newline at end of file
diff --git a/src/repositories/user.repository.js b/src/repositories/user.repository.js
index 3b6f051..1583579 100644
--- a/src/repositories/user.repository.js
+++ b/src/repositories/user.repository.js
@@ -591,6 +591,11 @@ export const findSelfLetters = async ({ userId, letterType }) => {
       createdAt: true,
       deliveredAt: true,
       questionId: true,
+      question: {
+        select: {
+          content: true
+        }
+      },
       design: {
         select: { 
           paperId: true,
diff --git a/src/services/mailbox.service.js b/src/services/mailbox.service.js
index 1e96796..0f17cf4 100644
--- a/src/services/mailbox.service.js
+++ b/src/services/mailbox.service.js
@@ -6,8 +6,15 @@ import {
 import { LETTER_TYPE_ANON, LETTER_TYPE_SELF, makePreview } from "../utils/user.util.js";
 import { findFriendById } from "../repositories/friend.repository.js";
 import { NotFriendError } from "../errors/friend.error.js";
-import { getFriendLetters, getMyLettersWithFriend } from "../repositories/letter.repository.js";
-import { prisma } from "../configs/db.config.js";
+import { 
+  getFriendLetters, 
+  getMyLettersWithFriend,
+  countLettersBySessionIdAndUserId,
+  countUnreadLettersBySessionIdAndUserId,
+  findReceivedLettersBySessionIdAndUserId,
+  findSentLettersBySessionIdAndUserId,
+} from "../repositories/letter.repository.js";
+import { findMatchingSessionBySessionIdAndUserId } from "../repositories/session.repository.js";
 import { MailboxInvalidSessionIdError } from "../errors/mailbox.error.js";
 
 // ------------------------------
@@ -62,15 +69,10 @@ export const getAnonymousThreads = async (userId) => {
   // 각 세션별 편지 개수 조회 (sessionId 기준, 개별 조회)
   const letterCounts = await Promise.all(
     sessionIds.map(async (sessionId) => {
-      const count = await prisma.letter.count({
-        where: {
-          letterType: LETTER_TYPE_ANON,
-          sessionId: sessionId,
-          OR: [
-            { receiverUserId: userId },
-            { senderUserId: userId }
-          ]
-        }
+      const count = await countLettersBySessionIdAndUserId({
+        sessionId,
+        userId,
+        letterType: LETTER_TYPE_ANON,
       });
       return [sessionId, count];
     })
@@ -80,13 +82,10 @@ export const getAnonymousThreads = async (userId) => {
   // 각 세션별 읽지 않은 편지 체크 (받은 편지만 체크)
   const unreadChecks = await Promise.all(
     sessionIds.map(async (sessionId) => {
-      const unreadCount = await prisma.letter.count({
-        where: {
-          letterType: LETTER_TYPE_ANON,
-          sessionId: sessionId,
-          receiverUserId: userId,
-          readAt: null, // 읽지 않은 편지
-        }
+      const unreadCount = await countUnreadLettersBySessionIdAndUserId({
+        sessionId,
+        userId,
+        letterType: LETTER_TYPE_ANON,
       });
       return [sessionId, unreadCount > 0]; // 하나라도 있으면 true
     })
@@ -129,22 +128,9 @@ export const getAnonymousThreadLetters = async (userId, sessionIdRaw) => {
   const sessionId = Number(sessionIdRaw);
 
   // 세션 참가자 조회하여 권한 확인
-  const session = await prisma.matchingSession.findFirst({
-    where: {
-      id: sessionId,
-      participants: {
-        some: {
-          userId: userId // 현재 사용자가 참가자인 세션만
-        }
-      }
-    },
-    include: {
-      participants: {
-        select: {
-          userId: true
-        }
-      }
-    }
+  const session = await findMatchingSessionBySessionIdAndUserId({
+    sessionId,
+    userId,
   });
 
   if (!session) {
@@ -152,81 +138,17 @@ export const getAnonymousThreadLetters = async (userId, sessionIdRaw) => {
   }
 
   // 받은 편지 조회 (sessionId로 필터링)
-  const receivedLetters = await prisma.letter.findMany({
-    where: {
-      receiverUserId: userId,
-      sessionId: sessionId,
-      letterType: LETTER_TYPE_ANON,
-    },
-    orderBy: [{ deliveredAt: "desc" }, { createdAt: "desc" }],
-    select: {
-      id: true,
-      title: true,
-      deliveredAt: true,
-      readAt: true,
-      createdAt: true,
-      question: {
-        select: {
-          content: true
-        }
-      },
-      design: {
-        select: {
-          paper: {
-            select: {
-              id: true,
-              color: true,
-            }
-          },
-          stamp: {
-            select: {
-              id: true,
-              name: true,
-              assetUrl: true
-            }
-          },
-        },
-      },
-    },
+  const receivedLetters = await findReceivedLettersBySessionIdAndUserId({
+    sessionId,
+    userId,
+    letterType: LETTER_TYPE_ANON,
   });
 
   // 보낸 편지 조회 (sessionId로 필터링)
-  const sentLetters = await prisma.letter.findMany({
-    where: {
-      senderUserId: userId,
-      sessionId: sessionId,
-      letterType: LETTER_TYPE_ANON,
-    },
-    orderBy: [{ deliveredAt: "desc" }, { createdAt: "desc" }],
-    select: {
-      id: true,
-      title: true,
-      deliveredAt: true,
-      readAt: true,
-      createdAt: true,
-      question: {
-        select: {
-          content: true
-        }
-      },
-      design: {
-        select: {
-          paper: {
-            select: {
-              id: true,
-              color: true,
-            }
-          },
-          stamp: {
-            select: {
-              id: true,
-              name: true,
-              assetUrl: true
-            }
-          },
-        },
-      },
-    },
+  const sentLetters = await findSentLettersBySessionIdAndUserId({
+    sessionId,
+    userId,
+    letterType: LETTER_TYPE_ANON,
   });
 
   // firstQuestion: 받은 편지의 첫 번째 질문 우선, 없으면 보낸 편지의 첫 번째 질문
@@ -296,7 +218,7 @@ export const getSelfMailbox = async (userId) => {
     id: l.id,
     title: l.title,
     createdAt: l.createdAt ?? null,
-    questionId: l.questionId ?? null,
+    questionTitle: l.question?.content ?? null,
     paperId: l.design?.paperId ?? null,
     stampId: l.design?.stampId ?? null,
     stampUrl: l.design?.stamp?.assetUrl ?? null,
diff --git a/src/swagger/mailbox.swagger.js b/src/swagger/mailbox.swagger.js
index 44a1ee3..3b1ffa5 100644
--- a/src/swagger/mailbox.swagger.js
+++ b/src/swagger/mailbox.swagger.js
@@ -522,9 +522,10 @@
  *                                 type: string
  *                                 format: date-time
  *                                 nullable: true
- *                               questionId:
- *                                 type: integer
+ *                               questionTitle:
+ *                                 type: string
  *                                 nullable: true
+ *                                 description: 질문 내용
  *                               paperId:
  *                                 type: integer
  *                                 nullable: true