diff --git a/src/main/java/postman/bottler/global/response/code/ErrorStatus.java b/src/main/java/postman/bottler/global/response/code/ErrorStatus.java
index 4e2d26c8..f6d63ca0 100644
--- a/src/main/java/postman/bottler/global/response/code/ErrorStatus.java
+++ b/src/main/java/postman/bottler/global/response/code/ErrorStatus.java
@@ -30,6 +30,8 @@ public enum ErrorStatus {
     REPLY_LETTER_VALIDATION_ERROR(HttpStatus.BAD_REQUEST, "REPLY_LETTER4001"),
     INVALID_LETTER_TYPE(HttpStatus.BAD_REQUEST, "LETTER_TYPE4000"),
     DUPLICATE_REPLY_LETTER(HttpStatus.BAD_REQUEST, "REPLY_LETTER4002"),
+    LETTER_AUTHOR_MISMATCH(HttpStatus.BAD_REQUEST, "LETTER4004"),
+    UNAUTHORIZED_LETTER_ACCESS(HttpStatus.UNAUTHORIZED, "LETTER4010"),
 
     // 추천 에러
     TEMP_RECOMMENDATIONS_NOT_FOUND(HttpStatus.NOT_FOUND, "TEMP_RECOMMENDATIONS_4040"),
diff --git a/src/main/java/postman/bottler/keyword/dto/response/KeywordResponseDTO.java b/src/main/java/postman/bottler/keyword/dto/response/KeywordResponseDTO.java
index 1e0b852a..6546e47f 100644
--- a/src/main/java/postman/bottler/keyword/dto/response/KeywordResponseDTO.java
+++ b/src/main/java/postman/bottler/keyword/dto/response/KeywordResponseDTO.java
@@ -8,16 +8,13 @@
 public record KeywordResponseDTO(
         List<CategoryKeywordsDTO> categories
 ) {
-    // 정적 팩토리 메서드로 변환 로직 처리
     public static KeywordResponseDTO from(List<Keyword> keywordList) {
-        // 카테고리별로 키워드 그룹화
         Map<String, List<String>> groupedByCategory = keywordList.stream()
                 .collect(Collectors.groupingBy(
                         Keyword::getCategory,
                         Collectors.mapping(Keyword::getKeyword, Collectors.toList())
                 ));
 
-        // 카테고리 DTO 리스트 생성
         List<CategoryKeywordsDTO> categories = groupedByCategory.entrySet().stream()
                 .map(entry -> new CategoryKeywordsDTO(entry.getKey(), entry.getValue()))
                 .toList();
diff --git a/src/main/java/postman/bottler/keyword/service/RedisLetterService.java b/src/main/java/postman/bottler/keyword/service/RedisLetterService.java
index dca08918..3b8e0a57 100644
--- a/src/main/java/postman/bottler/keyword/service/RedisLetterService.java
+++ b/src/main/java/postman/bottler/keyword/service/RedisLetterService.java
@@ -41,7 +41,7 @@ public RecommendNotificationRequestDTO updateRecommendationsFromTemp(Long userId
         Long recommendId = findFirstValidLetter(tempRecommendations);
         updateActiveRecommendations(recommendId, activeRecommendations, activeKey);
         saveLetterToBox(userId, recommendId);
-
+        
         redisTemplate.delete(tempKey);
 
         return RecommendNotificationRequestDTO.of(userId, recommendId);
diff --git a/src/main/java/postman/bottler/letter/controller/LetterBoxController.java b/src/main/java/postman/bottler/letter/controller/LetterBoxController.java
index 580f0165..ef1682f3 100644
--- a/src/main/java/postman/bottler/letter/controller/LetterBoxController.java
+++ b/src/main/java/postman/bottler/letter/controller/LetterBoxController.java
@@ -15,7 +15,7 @@
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 import postman.bottler.global.response.ApiResponse;
-import postman.bottler.letter.dto.request.LetterDeleteRequestDTO;
+import postman.bottler.letter.dto.LetterDeleteDTO;
 import postman.bottler.letter.dto.request.PageRequestDTO;
 import postman.bottler.letter.dto.response.LetterHeadersResponseDTO;
 import postman.bottler.letter.dto.response.PageResponseDTO;
@@ -39,6 +39,7 @@ public class LetterBoxController {
     @Operation(
             summary = "보관된 모든 편지 조회",
             description = "페이지네이션을 사용하여 보관된 모든 편지의 제목, 라벨이미지, 작성날짜 정보를 조회합니다."
+                    + "\nPage Default: page(1) size(9) sort(createAt)"
     )
     @GetMapping
     public ApiResponse<PageResponseDTO<LetterHeadersResponseDTO>> getAllLetters(
@@ -54,7 +55,8 @@ public ApiResponse<PageResponseDTO<LetterHeadersResponseDTO>> getAllLetters(
 
     @Operation(
             summary = "보낸 편지 조회",
-            description = "페이지네이션을 사용하여 보관된 보낸 편지의 헤더 정보를 조회합니다."
+            description = "페이지네이션을 사용하여 보관된 보낸 편지의 제목, 라벨이미지, 작성날짜 정보를 조회합니다."
+                    + "\nPage Default: page(1) size(9) sort(createAt)"
     )
     @GetMapping("/sent")
     public ApiResponse<PageResponseDTO<LetterHeadersResponseDTO>> getSentLetters(
@@ -71,6 +73,7 @@ public ApiResponse<PageResponseDTO<LetterHeadersResponseDTO>> getSentLetters(
     @Operation(
             summary = "받은 편지 조회",
             description = "페이지네이션을 사용하여 보관된 받은 편지의 제목, 라벨이미지, 작성날짜 정보를 조회합니다."
+                    + "\nPage Default: page(1) size(9) sort(createAt)"
     )
     @GetMapping("/received")
     public ApiResponse<PageResponseDTO<LetterHeadersResponseDTO>> getReceivedLetters(
@@ -90,9 +93,10 @@ public ApiResponse<PageResponseDTO<LetterHeadersResponseDTO>> getReceivedLetters
     )
     @DeleteMapping
     public ApiResponse<String> deleteSavedLetter(
-            @RequestBody @Valid List<LetterDeleteRequestDTO> letterDeleteRequestDTOS
+            @RequestBody @Valid List<LetterDeleteDTO> letterDeleteDTOS,
+            @AuthenticationPrincipal CustomUserDetails userDetails
     ) {
-        deleteManagerService.deleteLetters(letterDeleteRequestDTOS);
+        deleteManagerService.deleteLetters(letterDeleteDTOS, userDetails.getUserId());
         return ApiResponse.onSuccess("편지 보관을 취소했습니다.");
     }
 
diff --git a/src/main/java/postman/bottler/letter/controller/LetterController.java b/src/main/java/postman/bottler/letter/controller/LetterController.java
index 52acba86..7873d175 100644
--- a/src/main/java/postman/bottler/letter/controller/LetterController.java
+++ b/src/main/java/postman/bottler/letter/controller/LetterController.java
@@ -18,12 +18,14 @@
 import postman.bottler.keyword.service.LetterKeywordService;
 import postman.bottler.keyword.service.RedisLetterService;
 import postman.bottler.letter.domain.Letter;
+import postman.bottler.letter.dto.LetterDeleteDTO;
 import postman.bottler.letter.dto.request.LetterDeleteRequestDTO;
 import postman.bottler.letter.dto.request.LetterRequestDTO;
 import postman.bottler.letter.dto.response.LetterDetailResponseDTO;
 import postman.bottler.letter.dto.response.LetterRecommendHeadersResponseDTO;
 import postman.bottler.letter.exception.InvalidLetterRequestException;
 import postman.bottler.letter.service.DeleteManagerService;
+import postman.bottler.letter.service.LetterBoxService;
 import postman.bottler.letter.service.LetterService;
 import postman.bottler.letter.utiil.ValidationUtil;
 import postman.bottler.user.auth.CustomUserDetails;
@@ -39,6 +41,7 @@ public class LetterController {
     private final LetterKeywordService letterKeywordService;
     private final ValidationUtil validationUtil;
     private final RedisLetterService redisLetterService;
+    private final LetterBoxService letterBoxService;
 
     @Operation(
             summary = "키워드 편지 생성",
@@ -57,13 +60,14 @@ public ApiResponse<String> createLetter(
 
     @Operation(
             summary = "키워드 편지 삭제",
-            description = "키워드 편지ID, 편지타입(LETTER, REPLY_LETTER), 송수신 타입(SEND, RECEIVE)을 기반으로 키워드 편지를 삭제합니다."
+            description = "키워드 편지ID, BoxType 송수신(SEND, RECEIVE)을 기반으로 키워드 편지를 삭제합니다."
     )
     @DeleteMapping
     public ApiResponse<String> deleteLetter(
-            @RequestBody @Valid LetterDeleteRequestDTO letterDeleteRequestDTO
+            @RequestBody @Valid LetterDeleteRequestDTO letterDeleteRequestDTO,
+            @AuthenticationPrincipal CustomUserDetails userDetails
     ) {
-        deleteManagerService.deleteLetters(List.of(letterDeleteRequestDTO));
+        deleteManagerService.deleteLetter(LetterDeleteDTO.fromLetter(letterDeleteRequestDTO), userDetails.getUserId());
         return ApiResponse.onSuccess("키워드 편지를 삭제했습니다.");
     }
 
@@ -75,6 +79,7 @@ public ApiResponse<String> deleteLetter(
     public ApiResponse<LetterDetailResponseDTO> getLetter(
             @PathVariable Long letterId, @AuthenticationPrincipal CustomUserDetails userDetails
     ) {
+        letterBoxService.validateLetterInUserBox(letterId, userDetails.getUserId());
         List<String> keywords = letterKeywordService.getKeywords(letterId);
         LetterDetailResponseDTO result = letterService.getLetterDetail(letterId, keywords, userDetails.getUserId());
         return ApiResponse.onSuccess(result);
diff --git a/src/main/java/postman/bottler/letter/controller/ReplyLetterController.java b/src/main/java/postman/bottler/letter/controller/ReplyLetterController.java
index e9020e19..262716a6 100644
--- a/src/main/java/postman/bottler/letter/controller/ReplyLetterController.java
+++ b/src/main/java/postman/bottler/letter/controller/ReplyLetterController.java
@@ -3,7 +3,6 @@
 import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.validation.Valid;
-import java.util.List;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.data.domain.Page;
@@ -17,8 +16,9 @@
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 import postman.bottler.global.response.ApiResponse;
-import postman.bottler.letter.dto.request.LetterDeleteRequestDTO;
+import postman.bottler.letter.dto.LetterDeleteDTO;
 import postman.bottler.letter.dto.request.PageRequestDTO;
+import postman.bottler.letter.dto.request.ReplyLetterDeleteRequestDTO;
 import postman.bottler.letter.dto.request.ReplyLetterRequestDTO;
 import postman.bottler.letter.dto.response.PageResponseDTO;
 import postman.bottler.letter.dto.response.ReplyLetterHeadersResponseDTO;
@@ -26,6 +26,7 @@
 import postman.bottler.letter.exception.InvalidPageRequestException;
 import postman.bottler.letter.exception.InvalidReplyLetterRequestException;
 import postman.bottler.letter.service.DeleteManagerService;
+import postman.bottler.letter.service.LetterBoxService;
 import postman.bottler.letter.service.ReplyLetterService;
 import postman.bottler.letter.utiil.ValidationUtil;
 import postman.bottler.user.auth.CustomUserDetails;
@@ -40,6 +41,7 @@ public class ReplyLetterController {
     private final ReplyLetterService letterReplyService;
     private final DeleteManagerService deleteManagerService;
     private final ValidationUtil validationUtil;
+    private final LetterBoxService letterBoxService;
 
     @Operation(
             summary = "키워드 편지 생성",
@@ -61,6 +63,7 @@ public ApiResponse<ReplyLetterResponseDTO> createReply(
     @Operation(
             summary = "특정 키워드 편지에 대한 답장 목록 조회",
             description = "지정된 편지 ID에 대한 답장들의 제목, 라벨이미지, 작성날짜를 페이지네이션 형태로 반환합니다."
+                    + "\nPage Default: page(1) size(9) sort(createAt)"
     )
     @GetMapping("/{letterId}")
     public ApiResponse<PageResponseDTO<ReplyLetterHeadersResponseDTO>> getReplyForLetter(
@@ -69,6 +72,7 @@ public ApiResponse<PageResponseDTO<ReplyLetterHeadersResponseDTO>> getReplyForLe
             BindingResult bindingResult,
             @AuthenticationPrincipal CustomUserDetails userDetails
     ) {
+        letterBoxService.validateLetterInUserBox(letterId, userDetails.getUserId());
         validatePageRequest(bindingResult);
         Page<ReplyLetterHeadersResponseDTO> result =
                 letterReplyService.getReplyLetterHeadersById(letterId, pageRequestDTO, userDetails.getUserId());
@@ -81,21 +85,25 @@ public ApiResponse<PageResponseDTO<ReplyLetterHeadersResponseDTO>> getReplyForLe
     )
     @GetMapping("/detail/{replyLetterId}")
     public ApiResponse<ReplyLetterResponseDTO> getReplyLetter(
-            @PathVariable Long replyLetterId
+            @PathVariable Long replyLetterId,
+            @AuthenticationPrincipal CustomUserDetails userDetails
     ) {
+        letterBoxService.validateLetterInUserBox(replyLetterId, userDetails.getUserId());
         ReplyLetterResponseDTO result = letterReplyService.getReplyLetterDetail(replyLetterId);
         return ApiResponse.onSuccess(result);
     }
 
     @Operation(
             summary = "답장 편지 삭제",
-            description = "답장 편지ID, 편지타입(LETTER, REPLY_LETTER, 송수신 타입(SEND, RECEIVE)을 기반으로 답장 편지를 삭제합니다."
+            description = "답장 편지ID, 송수신 타입(SEND, RECEIVE)을 기반으로 답장 편지를 삭제합니다."
     )
     @DeleteMapping
     public ApiResponse<String> deleteReplyLetter(
-            @RequestBody @Valid LetterDeleteRequestDTO letterDeleteRequestDTO
+            @RequestBody @Valid ReplyLetterDeleteRequestDTO replyLetterDeleteRequestDTO,
+            @AuthenticationPrincipal CustomUserDetails userDetails
     ) {
-        deleteManagerService.deleteLetters(List.of(letterDeleteRequestDTO));
+        deleteManagerService.deleteLetter(LetterDeleteDTO.fromReplyLetter(replyLetterDeleteRequestDTO),
+                userDetails.getUserId());
         return ApiResponse.onSuccess("success");
     }
 
diff --git a/src/main/java/postman/bottler/letter/dto/LetterDeleteDTO.java b/src/main/java/postman/bottler/letter/dto/LetterDeleteDTO.java
new file mode 100644
index 00000000..5bc4c33e
--- /dev/null
+++ b/src/main/java/postman/bottler/letter/dto/LetterDeleteDTO.java
@@ -0,0 +1,29 @@
+package postman.bottler.letter.dto;
+
+import jakarta.validation.constraints.NotNull;
+import postman.bottler.letter.domain.BoxType;
+import postman.bottler.letter.domain.LetterType;
+import postman.bottler.letter.dto.request.LetterDeleteRequestDTO;
+import postman.bottler.letter.dto.request.ReplyLetterDeleteRequestDTO;
+
+public record LetterDeleteDTO(
+        @NotNull(message = "Letter ID는 필수입니다.") Long letterId,
+        @NotNull(message = "Letter Type은 필수입니다.") LetterType letterType,
+        @NotNull(message = "Box Type은 필수입니다.") BoxType boxType
+) {
+    public static LetterDeleteDTO fromLetter(LetterDeleteRequestDTO letterDeleteRequestDTO) {
+        return new LetterDeleteDTO(
+                letterDeleteRequestDTO.letterId(),
+                LetterType.LETTER,
+                letterDeleteRequestDTO.boxType()
+        );
+    }
+
+    public static LetterDeleteDTO fromReplyLetter(ReplyLetterDeleteRequestDTO replyLetterDeleteRequestDTO) {
+        return new LetterDeleteDTO(
+                replyLetterDeleteRequestDTO.letterId(),
+                LetterType.REPLY_LETTER,
+                replyLetterDeleteRequestDTO.boxType()
+        );
+    }
+}
diff --git a/src/main/java/postman/bottler/letter/dto/request/LetterDeleteRequestDTO.java b/src/main/java/postman/bottler/letter/dto/request/LetterDeleteRequestDTO.java
index 5ca100d0..17fbb9c8 100644
--- a/src/main/java/postman/bottler/letter/dto/request/LetterDeleteRequestDTO.java
+++ b/src/main/java/postman/bottler/letter/dto/request/LetterDeleteRequestDTO.java
@@ -2,18 +2,9 @@
 
 import jakarta.validation.constraints.NotNull;
 import postman.bottler.letter.domain.BoxType;
-import postman.bottler.letter.domain.LetterType;
 
 public record LetterDeleteRequestDTO(
         @NotNull(message = "Letter ID는 필수입니다.") Long letterId,
-        @NotNull(message = "Letter Type은 필수입니다.") LetterType letterType,
         @NotNull(message = "Box Type은 필수입니다.") BoxType boxType
 ) {
-    public static LetterDeleteRequestDTO of(Long letterId, LetterType letterType, BoxType boxType) {
-        return new LetterDeleteRequestDTO(
-                letterId,
-                letterType,
-                boxType
-        );
-    }
 }
diff --git a/src/main/java/postman/bottler/letter/dto/request/ReplyLetterDeleteRequestDTO.java b/src/main/java/postman/bottler/letter/dto/request/ReplyLetterDeleteRequestDTO.java
new file mode 100644
index 00000000..22ccd0a3
--- /dev/null
+++ b/src/main/java/postman/bottler/letter/dto/request/ReplyLetterDeleteRequestDTO.java
@@ -0,0 +1,16 @@
+package postman.bottler.letter.dto.request;
+
+import jakarta.validation.constraints.NotNull;
+import postman.bottler.letter.domain.BoxType;
+
+public record ReplyLetterDeleteRequestDTO(
+        @NotNull(message = "Letter ID는 필수입니다.") Long letterId,
+        @NotNull(message = "Box Type은 필수입니다.") BoxType boxType
+) {
+    public static ReplyLetterDeleteRequestDTO of(Long letterId, BoxType boxType) {
+        return new ReplyLetterDeleteRequestDTO(
+                letterId,
+                boxType
+        );
+    }
+}
diff --git a/src/main/java/postman/bottler/letter/exception/LetterAuthorMismatchException.java b/src/main/java/postman/bottler/letter/exception/LetterAuthorMismatchException.java
new file mode 100644
index 00000000..25f59d2c
--- /dev/null
+++ b/src/main/java/postman/bottler/letter/exception/LetterAuthorMismatchException.java
@@ -0,0 +1,7 @@
+package postman.bottler.letter.exception;
+
+public class LetterAuthorMismatchException extends RuntimeException {
+    public LetterAuthorMismatchException(String message) {
+        super(message);
+    }
+}
diff --git a/src/main/java/postman/bottler/letter/exception/LetterExceptionHandler.java b/src/main/java/postman/bottler/letter/exception/LetterExceptionHandler.java
index fa5cf895..f7cf31db 100644
--- a/src/main/java/postman/bottler/letter/exception/LetterExceptionHandler.java
+++ b/src/main/java/postman/bottler/letter/exception/LetterExceptionHandler.java
@@ -5,6 +5,7 @@
 import static postman.bottler.global.response.code.ErrorStatus.INVALID_SORT_FIELD;
 import static postman.bottler.global.response.code.ErrorStatus.LETTER_ACCESS_DENIED;
 import static postman.bottler.global.response.code.ErrorStatus.LETTER_ALREADY_SAVED;
+import static postman.bottler.global.response.code.ErrorStatus.LETTER_AUTHOR_MISMATCH;
 import static postman.bottler.global.response.code.ErrorStatus.LETTER_DELETE_VALIDATION_ERROR;
 import static postman.bottler.global.response.code.ErrorStatus.LETTER_NOT_FOUND;
 import static postman.bottler.global.response.code.ErrorStatus.LETTER_UNKNOWN_VALIDATION_ERROR;
@@ -12,6 +13,7 @@
 import static postman.bottler.global.response.code.ErrorStatus.PAGINATION_VALIDATION_ERROR;
 import static postman.bottler.global.response.code.ErrorStatus.REPLY_LETTER_VALIDATION_ERROR;
 import static postman.bottler.global.response.code.ErrorStatus.TEMP_RECOMMENDATIONS_NOT_FOUND;
+import static postman.bottler.global.response.code.ErrorStatus.UNAUTHORIZED_LETTER_ACCESS;
 
 import java.util.Map;
 import lombok.extern.slf4j.Slf4j;
@@ -114,4 +116,19 @@ public ResponseEntity<ApiResponse<String>> handleInvalidLetterTypeException(
                 .status(TEMP_RECOMMENDATIONS_NOT_FOUND.getHttpStatus())
                 .body(ApiResponse.onFailure(TEMP_RECOMMENDATIONS_NOT_FOUND.getCode(), e.getMessage(), null));
     }
+
+    @ExceptionHandler(LetterAuthorMismatchException.class)
+    public ResponseEntity<ApiResponse<String>> handleLetterAuthorMismatchException(LetterAuthorMismatchException e) {
+        return ResponseEntity
+                .status(LETTER_AUTHOR_MISMATCH.getHttpStatus())
+                .body(ApiResponse.onFailure(LETTER_AUTHOR_MISMATCH.getCode(), e.getMessage(), null));
+    }
+
+    @ExceptionHandler(UnauthorizedLetterAccessException.class)
+    public ResponseEntity<ApiResponse<String>> handleUnauthorizedLetterAccessException(
+            UnauthorizedLetterAccessException e) {
+        return ResponseEntity
+                .status(UNAUTHORIZED_LETTER_ACCESS.getHttpStatus())
+                .body(ApiResponse.onFailure(UNAUTHORIZED_LETTER_ACCESS.getCode(), e.getMessage(), null));
+    }
 }
diff --git a/src/main/java/postman/bottler/letter/exception/UnauthorizedLetterAccessException.java b/src/main/java/postman/bottler/letter/exception/UnauthorizedLetterAccessException.java
new file mode 100644
index 00000000..5bfef366
--- /dev/null
+++ b/src/main/java/postman/bottler/letter/exception/UnauthorizedLetterAccessException.java
@@ -0,0 +1,7 @@
+package postman.bottler.letter.exception;
+
+public class UnauthorizedLetterAccessException extends RuntimeException {
+    public UnauthorizedLetterAccessException(String message) {
+        super(message);
+    }
+}
diff --git a/src/main/java/postman/bottler/letter/infra/LetterBoxJdbcRepository.java b/src/main/java/postman/bottler/letter/infra/LetterBoxJdbcRepository.java
index 44ff58f2..d7b0a778 100644
--- a/src/main/java/postman/bottler/letter/infra/LetterBoxJdbcRepository.java
+++ b/src/main/java/postman/bottler/letter/infra/LetterBoxJdbcRepository.java
@@ -42,4 +42,11 @@ public void saveAll(List<LetterBox> letterBoxes) {
 
         jdbcTemplate.batchUpdate(sql, params);
     }
+
+    public boolean existsByUserIdAndLetterId(Long letterId, Long userId) {
+        String sql = "SELECT COUNT(*) FROM letter_box WHERE user_id = ? AND letter_id = ?";
+
+        Integer count = jdbcTemplate.queryForObject(sql, Integer.class, userId, letterId);
+        return count > 0;
+    }
 }
diff --git a/src/main/java/postman/bottler/letter/infra/LetterBoxQueryRepository.java b/src/main/java/postman/bottler/letter/infra/LetterBoxQueryRepository.java
index d8c38644..f20cd5d8 100644
--- a/src/main/java/postman/bottler/letter/infra/LetterBoxQueryRepository.java
+++ b/src/main/java/postman/bottler/letter/infra/LetterBoxQueryRepository.java
@@ -86,4 +86,17 @@ public void deleteByCondition(List<Long> letterIds, LetterType letterType, BoxTy
                 )
                 .execute();
     }
+
+    public void deleteByConditionAndUserId(List<Long> letterIds, LetterType letterType, BoxType boxType, Long userId) {
+        QLetterBoxEntity letterBox = QLetterBoxEntity.letterBoxEntity;
+
+        queryFactory.delete(letterBox)
+                .where(
+                        letterIds != null ? letterBox.letterId.in(letterIds) : null,
+                        letterType != LetterType.UNKNOWN ? letterBox.letterType.eq(letterType) : null,
+                        boxType != BoxType.UNKNOWN ? letterBox.boxType.eq(boxType) : null,
+                        letterBox.userId.eq(userId)
+                )
+                .execute();
+    }
 }
diff --git a/src/main/java/postman/bottler/letter/infra/LetterBoxRepositoryImpl.java b/src/main/java/postman/bottler/letter/infra/LetterBoxRepositoryImpl.java
index b8d58b00..1a9af7e9 100644
--- a/src/main/java/postman/bottler/letter/infra/LetterBoxRepositoryImpl.java
+++ b/src/main/java/postman/bottler/letter/infra/LetterBoxRepositoryImpl.java
@@ -52,14 +52,19 @@ public void deleteByCondition(List<Long> letterIds, LetterType letterType, BoxTy
         letterBoxQueryRepository.deleteByCondition(letterIds, letterType, boxType);
     }
 
+    @Override
+    public void deleteByConditionAndUserId(List<Long> letterIds, LetterType letterType, BoxType boxType, Long userId) {
+        letterBoxQueryRepository.deleteByConditionAndUserId(letterIds, letterType, boxType, userId);
+    }
+
     @Override
     public List<Long> getReceivedLettersById(Long userId) {
         return letterBoxQueryRepository.getReceivedLettersById(userId);
     }
 
     @Override
-    public void saveRecommendedLetters(List<LetterBox> letterBoxes) {
-        letterBoxJdbcRepository.saveAll(letterBoxes);
+    public boolean existsByLetterIdAndUserId(Long letterId, Long userId) {
+        return letterBoxJdbcRepository.existsByUserIdAndLetterId(letterId, userId);
     }
 
     private List<LetterHeadersResponseDTO> fetchLetters(Long userId, BoxType boxType, Pageable pageable) {
diff --git a/src/main/java/postman/bottler/letter/service/DeleteManagerService.java b/src/main/java/postman/bottler/letter/service/DeleteManagerService.java
index a949fcdf..0f4fb019 100644
--- a/src/main/java/postman/bottler/letter/service/DeleteManagerService.java
+++ b/src/main/java/postman/bottler/letter/service/DeleteManagerService.java
@@ -10,7 +10,7 @@
 import postman.bottler.keyword.service.LetterKeywordService;
 import postman.bottler.letter.domain.BoxType;
 import postman.bottler.letter.domain.LetterType;
-import postman.bottler.letter.dto.request.LetterDeleteRequestDTO;
+import postman.bottler.letter.dto.LetterDeleteDTO;
 
 @Slf4j
 @Service
@@ -22,27 +22,42 @@ public class DeleteManagerService {
     private final LetterKeywordService letterKeywordService;
 
     @Transactional
-    public void deleteLetters(List<LetterDeleteRequestDTO> letterDeleteRequestDTOs) {
-        Map<LetterType, Map<BoxType, List<Long>>> groupedByTypeAndBox = letterDeleteRequestDTOs.stream()
+    public void deleteLetter(LetterDeleteDTO letterDeleteDTO, Long userId) {
+        Map<LetterType, Map<BoxType, List<Long>>> groupedByTypeAndBox = Map.of(
+                letterDeleteDTO.letterType(),
+                Map.of(
+                        letterDeleteDTO.boxType(),
+                        List.of(letterDeleteDTO.letterId())
+                )
+        );
+        processGroupedLetters(groupedByTypeAndBox, userId);
+    }
+
+    @Transactional
+    public void deleteLetters(List<LetterDeleteDTO> letterDeleteDTOS, Long userId) {
+        Map<LetterType, Map<BoxType, List<Long>>> groupedByTypeAndBox = letterDeleteDTOS.stream()
                 .collect(Collectors.groupingBy(
-                        LetterDeleteRequestDTO::letterType,
+                        LetterDeleteDTO::letterType,
                         Collectors.groupingBy(
-                                LetterDeleteRequestDTO::boxType,
-                                Collectors.mapping(LetterDeleteRequestDTO::letterId, Collectors.toList())
+                                LetterDeleteDTO::boxType,
+                                Collectors.mapping(LetterDeleteDTO::letterId, Collectors.toList())
                         )
                 ));
+        processGroupedLetters(groupedByTypeAndBox, userId);
+    }
 
+    private void processGroupedLetters(Map<LetterType, Map<BoxType, List<Long>>> groupedByTypeAndBox, Long userId) {
         if (groupedByTypeAndBox.containsKey(LetterType.LETTER)) {
             Map<BoxType, List<Long>> letterBoxMap = groupedByTypeAndBox.get(LetterType.LETTER);
             if (letterBoxMap.containsKey(BoxType.SEND)) {
                 List<Long> letterIds = letterBoxMap.get(BoxType.SEND);
-                letterService.deleteLetters(letterIds); // LetterService에서 삭제
+                letterService.deleteLetters(letterIds, userId);
                 letterKeywordService.markKeywordsAsDeleted(letterIds);
                 letterBoxService.deleteByIdsAndType(letterIds, LetterType.LETTER, BoxType.UNKNOWN);
             }
             if (letterBoxMap.containsKey(BoxType.RECEIVE)) {
                 List<Long> letterIds = letterBoxMap.get(BoxType.RECEIVE);
-                letterBoxService.deleteByIdsAndType(letterIds, LetterType.LETTER, BoxType.RECEIVE);
+                letterBoxService.deleteByIdsAndTypeAndUserId(letterIds, LetterType.LETTER, BoxType.RECEIVE, userId);
             }
         }
 
@@ -50,13 +65,15 @@ public void deleteLetters(List<LetterDeleteRequestDTO> letterDeleteRequestDTOs)
             Map<BoxType, List<Long>> replyLetterBoxMap = groupedByTypeAndBox.get(LetterType.REPLY_LETTER);
             if (replyLetterBoxMap.containsKey(BoxType.SEND)) {
                 List<Long> replyLetterIds = replyLetterBoxMap.get(BoxType.SEND);
-                replyLetterService.deleteReplyLetters(replyLetterIds); // ReplyLetterService에서 삭제
+                replyLetterService.deleteReplyLetters(replyLetterIds, userId);
                 letterBoxService.deleteByIdsAndType(replyLetterIds, LetterType.REPLY_LETTER, BoxType.UNKNOWN);
             }
             if (replyLetterBoxMap.containsKey(BoxType.RECEIVE)) {
                 List<Long> replyLetterIds = replyLetterBoxMap.get(BoxType.RECEIVE);
-                letterBoxService.deleteByIdsAndType(replyLetterIds, LetterType.REPLY_LETTER, BoxType.RECEIVE);
+                letterBoxService.deleteByIdsAndTypeAndUserId(replyLetterIds, LetterType.REPLY_LETTER, BoxType.RECEIVE,
+                        userId);
             }
         }
     }
+
 }
diff --git a/src/main/java/postman/bottler/letter/service/LetterBoxRepository.java b/src/main/java/postman/bottler/letter/service/LetterBoxRepository.java
index 20f6002d..b0e1eb86 100644
--- a/src/main/java/postman/bottler/letter/service/LetterBoxRepository.java
+++ b/src/main/java/postman/bottler/letter/service/LetterBoxRepository.java
@@ -19,7 +19,9 @@ public interface LetterBoxRepository {
 
     void deleteByCondition(List<Long> letterIds, LetterType letterType, BoxType boxType);
 
+    void deleteByConditionAndUserId(List<Long> letterIds, LetterType letterType, BoxType boxType, Long userId);
+
     List<Long> getReceivedLettersById(Long userId);
 
-    void saveRecommendedLetters(List<LetterBox> letterBoxes);
+    boolean existsByLetterIdAndUserId(Long letterId, Long userId);
 }
diff --git a/src/main/java/postman/bottler/letter/service/LetterBoxService.java b/src/main/java/postman/bottler/letter/service/LetterBoxService.java
index b5967775..bc5b7a70 100644
--- a/src/main/java/postman/bottler/letter/service/LetterBoxService.java
+++ b/src/main/java/postman/bottler/letter/service/LetterBoxService.java
@@ -11,6 +11,7 @@
 import postman.bottler.letter.dto.LetterBoxDTO;
 import postman.bottler.letter.dto.request.PageRequestDTO;
 import postman.bottler.letter.dto.response.LetterHeadersResponseDTO;
+import postman.bottler.letter.exception.UnauthorizedLetterAccessException;
 
 @Slf4j
 @Service
@@ -44,9 +45,22 @@ public void deleteByIdsAndType(List<Long> letterIds, LetterType letterType, BoxT
         letterBoxRepository.deleteByCondition(letterIds, letterType, boxType);
     }
 
+    @Transactional
+    public void deleteByIdsAndTypeAndUserId(List<Long> letterIds, LetterType letterType, BoxType boxType, Long userId) {
+        letterBoxRepository.deleteByConditionAndUserId(letterIds, letterType, boxType, userId);
+    }
+
+
     @Transactional(readOnly = true)
     public List<Long> getLettersByUserId(Long userId) {
         return letterBoxRepository.getReceivedLettersById(userId);
     }
 
+    @Transactional(readOnly = true)
+    public void validateLetterInUserBox(Long letterId, Long userId) {
+        boolean isLetterInUserBox = letterBoxRepository.existsByLetterIdAndUserId(letterId, userId);
+        if (!isLetterInUserBox) {
+            throw new UnauthorizedLetterAccessException("사용자가 해당 편지에 접근할 권한이 없습니다.");
+        }
+    }
 }
diff --git a/src/main/java/postman/bottler/letter/service/LetterService.java b/src/main/java/postman/bottler/letter/service/LetterService.java
index 216d71c7..a96c9fd1 100644
--- a/src/main/java/postman/bottler/letter/service/LetterService.java
+++ b/src/main/java/postman/bottler/letter/service/LetterService.java
@@ -13,6 +13,7 @@
 import postman.bottler.letter.dto.request.LetterRequestDTO;
 import postman.bottler.letter.dto.response.LetterDetailResponseDTO;
 import postman.bottler.letter.dto.response.LetterRecommendHeadersResponseDTO;
+import postman.bottler.letter.exception.LetterAuthorMismatchException;
 import postman.bottler.letter.exception.LetterNotFoundException;
 import postman.bottler.notification.dto.request.NotificationLabelRequestDTO;
 import postman.bottler.user.service.UserService;
@@ -36,7 +37,12 @@ public Letter createLetter(LetterRequestDTO letterRequestDTO, Long userId) {
     }
 
     @Transactional
-    public void deleteLetters(List<Long> letterIds) {
+    public void deleteLetters(List<Long> letterIds, Long userId) {
+        letterIds.forEach(letterId -> {
+            if (!findLetter(letterId).getUserId().equals(userId)) {
+                throw new LetterAuthorMismatchException("요청자와 작성자가 일치하지 않습니다.");
+            }
+        });
         letterRepository.deleteByIds(letterIds);
     }
 
diff --git a/src/main/java/postman/bottler/letter/service/ReplyLetterService.java b/src/main/java/postman/bottler/letter/service/ReplyLetterService.java
index 6beb3c8a..1e1f614e 100644
--- a/src/main/java/postman/bottler/letter/service/ReplyLetterService.java
+++ b/src/main/java/postman/bottler/letter/service/ReplyLetterService.java
@@ -17,6 +17,7 @@
 import postman.bottler.letter.dto.response.ReplyLetterHeadersResponseDTO;
 import postman.bottler.letter.dto.response.ReplyLetterResponseDTO;
 import postman.bottler.letter.exception.DuplicateReplyLetterException;
+import postman.bottler.letter.exception.LetterAuthorMismatchException;
 import postman.bottler.letter.exception.LetterNotFoundException;
 import postman.bottler.reply.dto.ReplyType;
 
@@ -80,17 +81,20 @@ public ReplyLetterResponseDTO getReplyLetterDetail(Long replyLetterId) {
     }
 
     @Transactional
-    public void deleteReplyLetters(List<Long> letterIds) {
+    public void deleteReplyLetters(List<Long> letterIds, Long userId) {
+        letterIds.forEach(letterId -> {
+            if (!findReplyLetter(letterId).getSenderId().equals(userId)) {
+                throw new LetterAuthorMismatchException("요청자와 작성자가 일치하지 않습니다.");
+            }
+        });
+        letterIds.forEach(this::deleteRecentReply);
         replyLetterRepository.deleteByIds(letterIds);
-        for (Long letterId : letterIds) {
-            deleteRecentReply(letterId);
-        }
     }
 
     @Transactional
     public Long blockLetter(Long replyLetterId) {
-        replyLetterRepository.blockReplyLetterById(replyLetterId);
         ReplyLetter replyLetter = findReplyLetter(replyLetterId);
+        replyLetterRepository.blockReplyLetterById(replyLetterId);
         return replyLetter.getSenderId();
     }