diff --git a/internal/httpapi/handlers_projects.go b/internal/httpapi/handlers_projects.go
index 9e33017..08bc1cf 100644
--- a/internal/httpapi/handlers_projects.go
+++ b/internal/httpapi/handlers_projects.go
@@ -507,38 +507,41 @@ func (s *Server) handleListProjectMails(w http.ResponseWriter, r *http.Request)
 		writeJSON(w, http.StatusOK, resp)
 		return
 	}
+	// The cache holds the COMPANY-WIDE aggregate for the domain; we then filter
+	// per-viewer below (a member only sees mail they're a party to).
+	var agg []mailsync.Message
 	if v, ok := s.mailCache.Load(id); ok {
 		if e := v.(*mailCacheEntry); time.Since(e.at) < mailCacheTTL {
-			resp["messages"] = e.msgs
-			writeJSON(w, http.StatusOK, resp)
-			return
+			agg = e.msgs
 		}
 	}
-	// impersonation set = project members + PM (the team that corresponds with the client)
-	var pms []models.ProjectMember
-	s.db.Where("project_id = ?", id).Find(&pms)
-	set := map[string]bool{}
-	for _, m := range pms {
-		if m.MemberEmail != "" {
-			set[m.MemberEmail] = true
+	if agg == nil {
+		// 전사 모든 구성원 메일함을 impersonate해 도메인 메일을 모은다(구성원은 여러
+		// 프로젝트에 걸쳐 있으므로 전사 수집 후 프로젝트 도메인으로 필터하는 편이 단순).
+		var mailboxes []string
+		s.db.Model(&models.Member{}).Where("status <> ?", "inactive").Pluck("email", &mailboxes)
+		msgs, err := s.mail.ListForDomain(r.Context(), mailboxes, p.ClientDomain, 200)
+		if err != nil {
+			resp["error"] = err.Error()
+		}
+		if msgs == nil {
+			msgs = []mailsync.Message{}
+		}
+		agg = msgs
+		s.mailCache.Store(id, &mailCacheEntry{at: time.Now(), msgs: agg})
+	}
+	// per-viewer visibility: only mail the requester sent/received/was CC'd on.
+	me := s.email(r)
+	visible := make([]mailsync.Message, 0, len(agg))
+	for _, m := range agg {
+		if m.Involves(me) {
+			visible = append(visible, m)
+		}
+		if len(visible) >= 80 {
+			break
 		}
 	}
-	if p.PMEmail != "" {
-		set[p.PMEmail] = true
-	}
-	mailboxes := make([]string, 0, len(set))
-	for e := range set {
-		mailboxes = append(mailboxes, e)
-	}
-	msgs, err := s.mail.ListForDomain(r.Context(), mailboxes, p.ClientDomain, 60)
-	if err != nil {
-		resp["error"] = err.Error()
-	}
-	if msgs == nil {
-		msgs = []mailsync.Message{}
-	}
-	resp["messages"] = msgs
-	s.mailCache.Store(id, &mailCacheEntry{at: time.Now(), msgs: msgs})
+	resp["messages"] = visible
 	writeJSON(w, http.StatusOK, resp)
 }
 
diff --git a/internal/mailsync/mailsync.go b/internal/mailsync/mailsync.go
index aefa00e..53e661b 100644
--- a/internal/mailsync/mailsync.go
+++ b/internal/mailsync/mailsync.go
@@ -47,6 +47,7 @@ type Message struct {
 	ThreadID string `json:"threadId"`
 	From     string `json:"from"`
 	To       string `json:"to"`
+	Cc       string `json:"cc"`
 	Subject  string `json:"subject"`
 	Date     string `json:"date"`    // raw Date header
 	Snippet  string `json:"snippet"`
@@ -54,6 +55,16 @@ type Message struct {
 	TS       int64  `json:"ts"`      // internalDate (ms) for sorting/formatting
 }
 
+// Involves reports whether the given email appears in From/To/Cc (case-insensitive).
+// Used to gate per-viewer visibility: a member only sees mail they're a party to.
+func (m Message) Involves(email string) bool {
+	if email == "" {
+		return false
+	}
+	hay := strings.ToLower(m.From + " " + m.To + " " + m.Cc)
+	return strings.Contains(hay, strings.ToLower(email))
+}
+
 type tokenEntry struct {
 	token   string
 	expires time.Time
@@ -187,7 +198,7 @@ func (s *Service) getMeta(ctx context.Context, subject, id string) (Message, err
 	if err != nil {
 		return Message{}, err
 	}
-	u := fmt.Sprintf("https://gmail.googleapis.com/gmail/v1/users/me/messages/%s?format=metadata&metadataHeaders=From&metadataHeaders=To&metadataHeaders=Subject&metadataHeaders=Date&metadataHeaders=Message-ID", id)
+	u := fmt.Sprintf("https://gmail.googleapis.com/gmail/v1/users/me/messages/%s?format=metadata&metadataHeaders=From&metadataHeaders=To&metadataHeaders=Cc&metadataHeaders=Subject&metadataHeaders=Date&metadataHeaders=Message-ID", id)
 	req, _ := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
 	req.Header.Set("Authorization", "Bearer "+tok)
 	resp, err := s.client.Do(req)
@@ -220,6 +231,8 @@ func (s *Service) getMeta(ctx context.Context, subject, id string) (Message, err
 			m.From = h.Value
 		case "to":
 			m.To = h.Value
+		case "cc":
+			m.Cc = h.Value
 		case "subject":
 			m.Subject = h.Value
 		case "date":