diff --git a/cmd/server/main.go b/cmd/server/main.go
index e2d4fb0..66ce117 100644
--- a/cmd/server/main.go
+++ b/cmd/server/main.go
@@ -9,6 +9,7 @@ import (
 	"spin/internal/config"
 	"spin/internal/db"
 	"spin/internal/httpapi"
+	"spin/internal/mailsync"
 	"spin/internal/push"
 	"spin/internal/seed"
 	"spin/internal/storage"
@@ -46,7 +47,8 @@ func main() {
 	}
 
 	pusher := push.New(cfg.FCMCredentialsFile)
-	router := httpapi.NewRouter(gdb, store, cfg, pusher)
+	mailer := mailsync.New(cfg.GoogleSACredentialsFile)
+	router := httpapi.NewRouter(gdb, store, cfg, pusher, mailer)
 
 	addr := ":" + cfg.Port
 	srv := &http.Server{
diff --git a/internal/config/config.go b/internal/config/config.go
index db8845a..7552560 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -27,6 +27,10 @@ type Config struct {
 	// FCMCredentialsFile is the path to a Firebase service-account JSON used to
 	// send push notifications to spin-mobile. Empty = push disabled (no-op).
 	FCMCredentialsFile string
+	// GoogleSACredentialsFile is the path to a Google Workspace service-account
+	// JSON with DOMAIN-WIDE DELEGATION (gmail.readonly) used to read project
+	// client-domain mail. Empty = mail integration disabled.
+	GoogleSACredentialsFile string
 	// LogoutURL is the common SSO logout path injected by infra (LOGOUT_URL):
 	// ends the oauth2-proxy session then redirects to Keycloak end-session.
 	// The static frontend reads it via /me. Defaults to the infra-common value.
@@ -77,7 +81,8 @@ func Load() Config {
 		// Super-admin Keycloak groups (comma-separated). Default: admin
 		// (shared group name across all internal apps, not app-specific).
 		AdminGroups:        splitCSV(env("ADMIN_GROUPS", "admin")),
-		FCMCredentialsFile: env("FCM_CREDENTIALS_FILE", ""),
+		FCMCredentialsFile:      env("FCM_CREDENTIALS_FILE", ""),
+		GoogleSACredentialsFile: env("GOOGLE_SA_CREDENTIALS_FILE", ""),
 		LogoutURL: env("LOGOUT_URL",
 			"/oauth2/sign_out?rd=https%3A%2F%2Fauth.special-partners.com%2Frealms%2Fsp%2Fprotocol%2Fopenid-connect%2Flogout"),
 	}
diff --git a/internal/httpapi/handlers_projects.go b/internal/httpapi/handlers_projects.go
index 2889f62..9e33017 100644
--- a/internal/httpapi/handlers_projects.go
+++ b/internal/httpapi/handlers_projects.go
@@ -7,6 +7,7 @@ import (
 	"strings"
 	"time"
 
+	"spin/internal/mailsync"
 	"spin/internal/models"
 
 	"github.com/go-chi/chi/v5"
@@ -228,6 +229,9 @@ func (s *Server) handlePatchProject(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	delete(patch, "id")
+	// JSON 키(camelCase)를 DB 컬럼(snake_case)으로 변환해야 멀티워드 필드
+	// (consultingType·scopeText·pmEmail·clientDomain·startDate 등)가 저장된다.
+	patch = snakeKeys(patch)
 	if err := s.db.Model(&p).Updates(patch).Error; err != nil {
 		writeError(w, http.StatusInternalServerError, err.Error())
 		return
@@ -236,6 +240,28 @@ func (s *Server) handlePatchProject(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, p)
 }
 
+// snakeKeys converts camelCase JSON map keys to snake_case DB column names so
+// GORM Updates(map) targets the right columns. Safe for camelCase keys (no
+// leading/consecutive capitals), which is how all our JSON tags are written.
+func snakeKeys(m map[string]interface{}) map[string]interface{} {
+	out := make(map[string]interface{}, len(m))
+	for k, v := range m {
+		var b strings.Builder
+		for i, r := range k {
+			if r >= 'A' && r <= 'Z' {
+				if i > 0 {
+					b.WriteByte('_')
+				}
+				b.WriteRune(r - 'A' + 'a')
+			} else {
+				b.WriteRune(r)
+			}
+		}
+		out[b.String()] = v
+	}
+	return out
+}
+
 func (s *Server) handleDeleteProject(w http.ResponseWriter, r *http.Request) {
 	if !s.requireAdmin(w, r) {
 		return
@@ -384,6 +410,7 @@ func (s *Server) handlePatchTask(w http.ResponseWriter, r *http.Request) {
 			}
 		}
 	}
+	patch = snakeKeys(patch)
 	s.db.Model(&t).Updates(patch)
 	s.db.First(&t, "id = ?", t.ID)
 	writeJSON(w, http.StatusOK, t)
@@ -448,6 +475,118 @@ func (s *Server) handleDeleteTaskComment(w http.ResponseWriter, r *http.Request)
 	writeJSON(w, http.StatusOK, map[string]bool{"ok": true})
 }
 
+// ---- project mail (Google Workspace 도메인 위임) + 공동 메모 -----------------
+
+type mailCacheEntry struct {
+	at   time.Time
+	msgs []mailsync.Message
+}
+
+const mailCacheTTL = 3 * time.Minute
+
+// handleListProjectMails aggregates client-domain mail across the project team's
+// mailboxes (service account + domain-wide delegation). Disabled/empty-domain
+// projects return an empty list with flags so the UI can explain.
+func (s *Server) handleListProjectMails(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	if !s.canSeeProject(r, id) {
+		writeError(w, http.StatusForbidden, "권한이 없습니다")
+		return
+	}
+	var p models.Project
+	if err := s.db.First(&p, "id = ?", id).Error; err != nil {
+		writeError(w, http.StatusNotFound, "프로젝트를 찾을 수 없습니다")
+		return
+	}
+	resp := map[string]any{
+		"enabled":  s.mail.Enabled(),
+		"domain":   p.ClientDomain,
+		"messages": []mailsync.Message{},
+	}
+	if !s.mail.Enabled() || strings.TrimSpace(p.ClientDomain) == "" {
+		writeJSON(w, http.StatusOK, resp)
+		return
+	}
+	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
+		}
+	}
+	// 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 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})
+	writeJSON(w, http.StatusOK, resp)
+}
+
+func (s *Server) handleListMailNotes(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	if !s.canSeeProject(r, id) {
+		writeError(w, http.StatusForbidden, "권한이 없습니다")
+		return
+	}
+	var out []models.MailNote
+	s.db.Where("project_id = ?", id).Find(&out)
+	writeJSON(w, http.StatusOK, out)
+}
+
+// handlePutMailNote upserts the shared memo for one email. Any project member may
+// edit it; the message id travels in the body (Message-ID contains <>@ chars).
+func (s *Server) handlePutMailNote(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	if !s.canSeeProject(r, id) {
+		writeError(w, http.StatusForbidden, "권한이 없습니다")
+		return
+	}
+	var in struct {
+		MessageID string `json:"messageId"`
+		Body      string `json:"body"`
+	}
+	if err := decodeJSON(r, &in); err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	if strings.TrimSpace(in.MessageID) == "" {
+		writeError(w, http.StatusBadRequest, "messageId가 필요합니다")
+		return
+	}
+	var note models.MailNote
+	err := s.db.Where("project_id = ? AND message_id = ?", id, in.MessageID).First(&note).Error
+	note.Body = in.Body
+	note.LastEditedBy = s.email(r)
+	if err != nil { // not found → create
+		note.ProjectID = id
+		note.MessageID = in.MessageID
+		s.db.Create(&note)
+	} else {
+		s.db.Model(&note).Updates(map[string]interface{}{"body": note.Body, "last_edited_by": note.LastEditedBy})
+	}
+	writeJSON(w, http.StatusOK, note)
+}
+
 func (s *Server) handleDeleteTask(w http.ResponseWriter, r *http.Request) {
 	var t models.ProjectTask
 	if err := s.db.First(&t, "id = ?", chi.URLParam(r, "tId")).Error; err != nil {
diff --git a/internal/httpapi/router.go b/internal/httpapi/router.go
index 12c17d5..77bf972 100644
--- a/internal/httpapi/router.go
+++ b/internal/httpapi/router.go
@@ -3,8 +3,10 @@ package httpapi
 import (
 	"encoding/json"
 	"net/http"
+	"sync"
 
 	"spin/internal/config"
+	"spin/internal/mailsync"
 	"spin/internal/push"
 	"spin/internal/storage"
 
@@ -16,15 +18,17 @@ import (
 
 // Server bundles dependencies shared by all handlers.
 type Server struct {
-	db    *gorm.DB
-	store *storage.Storage
-	cfg   config.Config
-	push  *push.Sender
+	db        *gorm.DB
+	store     *storage.Storage
+	cfg       config.Config
+	push      *push.Sender
+	mail      *mailsync.Service
+	mailCache sync.Map // projectID -> *mailCacheEntry (short-TTL aggregated mail)
 }
 
 // NewRouter wires up the chi router and mounts the /api routes for every module.
-func NewRouter(db *gorm.DB, store *storage.Storage, cfg config.Config, pusher *push.Sender) http.Handler {
-	s := &Server{db: db, store: store, cfg: cfg, push: pusher}
+func NewRouter(db *gorm.DB, store *storage.Storage, cfg config.Config, pusher *push.Sender, mailer *mailsync.Service) http.Handler {
+	s := &Server{db: db, store: store, cfg: cfg, push: pusher, mail: mailer}
 
 	r := chi.NewRouter()
 	r.Use(middleware.RequestID)
@@ -127,6 +131,10 @@ func NewRouter(db *gorm.DB, store *storage.Storage, cfg config.Config, pusher *p
 			r.Get("/tasks/{tId}/comments", s.handleListTaskComments)
 			r.Post("/tasks/{tId}/comments", s.handleCreateTaskComment)
 			r.Delete("/comments/{cId}", s.handleDeleteTaskComment)
+			// project mail (Google Workspace 도메인 위임) + 공동 메모
+			r.Get("/projects/{id}/mails", s.handleListProjectMails)
+			r.Get("/projects/{id}/mail-notes", s.handleListMailNotes)
+			r.Put("/projects/{id}/mail-notes", s.handlePutMailNote)
 			// admin-only commercial block
 			r.Get("/projects/{id}/contract", s.handleGetContract)
 			r.Put("/projects/{id}/contract", s.handlePutContract)
diff --git a/internal/mailsync/mailsync.go b/internal/mailsync/mailsync.go
new file mode 100644
index 0000000..aefa00e
--- /dev/null
+++ b/internal/mailsync/mailsync.go
@@ -0,0 +1,317 @@
+// Package mailsync reads Gmail messages for a project's client domain using a
+// Google Workspace service account with DOMAIN-WIDE DELEGATION — stdlib only, no
+// third-party SDK (mirrors internal/push for the JWT/OAuth dance).
+//
+// It is OPTIONAL: with no credentials configured the Service is "disabled" and
+// list calls return empty. This lets spin run without Google until the Workspace
+// admin provisions a service account + domain-wide delegation (gmail.readonly).
+//
+// For a project the handler passes the set of member emails to impersonate; for
+// each we mint a delegated token (sub=member) and search that mailbox for the
+// client domain, then aggregate + dedup by RFC822 Message-ID across the team.
+package mailsync
+
+import (
+	"context"
+	"crypto"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"encoding/base64"
+	"encoding/json"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"log"
+	"net/http"
+	"net/url"
+	"os"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+)
+
+const gmailScope = "https://www.googleapis.com/auth/gmail.readonly"
+
+type serviceAccount struct {
+	ProjectID   string `json:"project_id"`
+	PrivateKey  string `json:"private_key"`
+	ClientEmail string `json:"client_email"`
+	TokenURI    string `json:"token_uri"`
+}
+
+// Message is a slim mail summary surfaced to the project mail tab.
+type Message struct {
+	ID       string `json:"id"`       // RFC822 Message-ID (stable dedup key)
+	ThreadID string `json:"threadId"`
+	From     string `json:"from"`
+	To       string `json:"to"`
+	Subject  string `json:"subject"`
+	Date     string `json:"date"`    // raw Date header
+	Snippet  string `json:"snippet"`
+	Mailbox  string `json:"mailbox"` // whose mailbox surfaced it
+	TS       int64  `json:"ts"`      // internalDate (ms) for sorting/formatting
+}
+
+type tokenEntry struct {
+	token   string
+	expires time.Time
+}
+
+// Service holds the delegated service-account credentials and a per-subject
+// (impersonated user) access-token cache.
+type Service struct {
+	sa     *serviceAccount
+	key    *rsa.PrivateKey
+	client *http.Client
+	mu     sync.Mutex
+	tokens map[string]tokenEntry
+}
+
+// New builds a Service from a service-account JSON file path. Empty path or a
+// read/parse error yields a disabled Service.
+func New(credsPath string) *Service {
+	if strings.TrimSpace(credsPath) == "" {
+		log.Printf("mailsync: Gmail disabled (no credentials configured)")
+		return &Service{}
+	}
+	raw, err := os.ReadFile(credsPath)
+	if err != nil {
+		log.Printf("mailsync: Gmail disabled (cannot read %s: %v)", credsPath, err)
+		return &Service{}
+	}
+	var sa serviceAccount
+	if err := json.Unmarshal(raw, &sa); err != nil || sa.PrivateKey == "" || sa.ClientEmail == "" {
+		log.Printf("mailsync: Gmail disabled (invalid service account JSON)")
+		return &Service{}
+	}
+	key, err := parsePrivateKey(sa.PrivateKey)
+	if err != nil {
+		log.Printf("mailsync: Gmail disabled (bad private key: %v)", err)
+		return &Service{}
+	}
+	if sa.TokenURI == "" {
+		sa.TokenURI = "https://oauth2.googleapis.com/token"
+	}
+	log.Printf("mailsync: Gmail enabled (sa=%s)", sa.ClientEmail)
+	return &Service{sa: &sa, key: key, client: &http.Client{Timeout: 15 * time.Second}, tokens: map[string]tokenEntry{}}
+}
+
+// Enabled reports whether real Gmail access is configured.
+func (s *Service) Enabled() bool { return s != nil && s.sa != nil }
+
+// ListForDomain impersonates each mailbox in turn, searches it for the client
+// domain, and returns the aggregated, de-duplicated, newest-first list (<= max).
+func (s *Service) ListForDomain(ctx context.Context, mailboxes []string, domain string, max int) ([]Message, error) {
+	if !s.Enabled() {
+		return nil, nil
+	}
+	domain = strings.TrimSpace(strings.TrimPrefix(domain, "@"))
+	if domain == "" {
+		return nil, nil
+	}
+	perBox := 25
+	q := fmt.Sprintf("(from:%s OR to:%s OR cc:%s) -in:chats", domain, domain, domain)
+	seen := map[string]bool{}
+	var all []Message
+	var firstErr error
+	for _, box := range mailboxes {
+		box = strings.TrimSpace(box)
+		if box == "" {
+			continue
+		}
+		ids, err := s.listIDs(ctx, box, q, perBox)
+		if err != nil {
+			if firstErr == nil {
+				firstErr = err
+			}
+			continue
+		}
+		for _, id := range ids {
+			m, err := s.getMeta(ctx, box, id)
+			if err != nil {
+				continue
+			}
+			key := m.ID
+			if key == "" {
+				key = box + "/" + id
+			}
+			if seen[key] {
+				continue
+			}
+			seen[key] = true
+			all = append(all, m)
+		}
+	}
+	sort.Slice(all, func(i, j int) bool { return all[i].TS > all[j].TS })
+	if max > 0 && len(all) > max {
+		all = all[:max]
+	}
+	return all, firstErr
+}
+
+func (s *Service) listIDs(ctx context.Context, subject, q string, max int) ([]string, error) {
+	tok, err := s.accessToken(ctx, subject)
+	if err != nil {
+		return nil, err
+	}
+	u := fmt.Sprintf("https://gmail.googleapis.com/gmail/v1/users/me/messages?maxResults=%d&q=%s", max, url.QueryEscape(q))
+	req, _ := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+	req.Header.Set("Authorization", "Bearer "+tok)
+	resp, err := s.client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode >= 300 {
+		return nil, fmt.Errorf("gmail list %d for %s", resp.StatusCode, subject)
+	}
+	var out struct {
+		Messages []struct {
+			ID string `json:"id"`
+		} `json:"messages"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		return nil, err
+	}
+	ids := make([]string, 0, len(out.Messages))
+	for _, m := range out.Messages {
+		ids = append(ids, m.ID)
+	}
+	return ids, nil
+}
+
+func (s *Service) getMeta(ctx context.Context, subject, id string) (Message, error) {
+	tok, err := s.accessToken(ctx, subject)
+	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)
+	req, _ := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+	req.Header.Set("Authorization", "Bearer "+tok)
+	resp, err := s.client.Do(req)
+	if err != nil {
+		return Message{}, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode >= 300 {
+		return Message{}, fmt.Errorf("gmail get %d", resp.StatusCode)
+	}
+	var out struct {
+		ID           string `json:"id"`
+		ThreadID     string `json:"threadId"`
+		Snippet      string `json:"snippet"`
+		InternalDate string `json:"internalDate"`
+		Payload      struct {
+			Headers []struct {
+				Name  string `json:"name"`
+				Value string `json:"value"`
+			} `json:"headers"`
+		} `json:"payload"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		return Message{}, err
+	}
+	m := Message{ThreadID: out.ThreadID, Snippet: out.Snippet, Mailbox: subject}
+	for _, h := range out.Payload.Headers {
+		switch strings.ToLower(h.Name) {
+		case "from":
+			m.From = h.Value
+		case "to":
+			m.To = h.Value
+		case "subject":
+			m.Subject = h.Value
+		case "date":
+			m.Date = h.Value
+		case "message-id":
+			m.ID = h.Value
+		}
+	}
+	if m.ID == "" {
+		m.ID = subject + "/" + out.ID
+	}
+	fmt.Sscan(out.InternalDate, &m.TS)
+	return m, nil
+}
+
+// accessToken returns a cached delegated token for the given subject (impersonated
+// user), minting a new one via the service-account JWT grant when expired.
+func (s *Service) accessToken(ctx context.Context, subject string) (string, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if e, ok := s.tokens[subject]; ok && e.token != "" && time.Now().Before(e.expires.Add(-60*time.Second)) {
+		return e.token, nil
+	}
+	now := time.Now()
+	claims := map[string]any{
+		"iss":   s.sa.ClientEmail,
+		"sub":   subject, // domain-wide delegation: act as this Workspace user
+		"scope": gmailScope,
+		"aud":   s.sa.TokenURI,
+		"iat":   now.Unix(),
+		"exp":   now.Add(time.Hour).Unix(),
+	}
+	assertion, err := s.signJWT(claims)
+	if err != nil {
+		return "", err
+	}
+	form := url.Values{}
+	form.Set("grant_type", "urn:ietf:params:oauth:grant-type:jwt-bearer")
+	form.Set("assertion", assertion)
+	req, _ := http.NewRequestWithContext(ctx, http.MethodPost, s.sa.TokenURI, strings.NewReader(form.Encode()))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	resp, err := s.client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+	var out struct {
+		AccessToken string `json:"access_token"`
+		ExpiresIn   int    `json:"expires_in"`
+		Error       string `json:"error"`
+		ErrorDesc   string `json:"error_description"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		return "", err
+	}
+	if out.AccessToken == "" {
+		return "", fmt.Errorf("token exchange failed for %s: %s %s", subject, out.Error, out.ErrorDesc)
+	}
+	s.tokens[subject] = tokenEntry{token: out.AccessToken, expires: now.Add(time.Duration(out.ExpiresIn) * time.Second)}
+	return out.AccessToken, nil
+}
+
+func (s *Service) signJWT(claims map[string]any) (string, error) {
+	header := map[string]string{"alg": "RS256", "typ": "JWT"}
+	hb, _ := json.Marshal(header)
+	cb, _ := json.Marshal(claims)
+	signingInput := b64(hb) + "." + b64(cb)
+	h := sha256.Sum256([]byte(signingInput))
+	sig, err := rsa.SignPKCS1v15(nil, s.key, crypto.SHA256, h[:])
+	if err != nil {
+		return "", err
+	}
+	return signingInput + "." + base64.RawURLEncoding.EncodeToString(sig), nil
+}
+
+func b64(b []byte) string { return base64.RawURLEncoding.EncodeToString(b) }
+
+func parsePrivateKey(pemStr string) (*rsa.PrivateKey, error) {
+	block, _ := pem.Decode([]byte(pemStr))
+	if block == nil {
+		return nil, errors.New("no PEM block")
+	}
+	if k, err := x509.ParsePKCS1PrivateKey(block.Bytes); err == nil {
+		return k, nil
+	}
+	keyAny, err := x509.ParsePKCS8PrivateKey(block.Bytes)
+	if err != nil {
+		return nil, err
+	}
+	k, ok := keyAny.(*rsa.PrivateKey)
+	if !ok {
+		return nil, errors.New("not an RSA private key")
+	}
+	return k, nil
+}
diff --git a/internal/models/models.go b/internal/models/models.go
index 146cc7d..1eca2eb 100644
--- a/internal/models/models.go
+++ b/internal/models/models.go
@@ -28,7 +28,7 @@ func All() []interface{} {
 		&Attendance{}, &LeaveRequest{}, &OvertimeRequest{}, &WorkPolicy{}, &LeaveBalance{},
 		// slice 3 — projects
 		&Company{}, &Product{}, &Version{}, &Project{}, &ProjectMember{},
-		&ClientContact{}, &ProjectTask{}, &TaskComment{}, &Contract{}, &ContractFile{}, &PaymentSplit{},
+		&ClientContact{}, &ProjectTask{}, &TaskComment{}, &MailNote{}, &Contract{}, &ContractFile{}, &PaymentSplit{},
 		// slice 4 — incentive
 		&IncentiveConfig{}, &PaymentStage{}, &UserIncentive{}, &QuarterlySettlement{},
 		// slice 5 — accounting
diff --git a/internal/models/project.go b/internal/models/project.go
index 67d4d5e..b129513 100644
--- a/internal/models/project.go
+++ b/internal/models/project.go
@@ -56,6 +56,7 @@ type Project struct {
 	ScopeText      string    `json:"scopeText"`      // 글 계약 범위
 	ScopeGraphic   string    `json:"scopeGraphic"`   // 그림 계약 범위
 	PMEmail        string    `json:"pmEmail"`        // 프로젝트 PM
+	ClientDomain   string    `json:"clientDomain"`   // 고객사 메일 도메인(postfix) — 관련 메일 집계용
 	Cautions       string    `json:"cautions"`       // 주의사항 (구성원 공개)
 	Status         string    `json:"status"`         // planned | active | hold | done | dropped
 	StartDate      string    `json:"startDate"`
@@ -125,6 +126,20 @@ type TaskComment struct {
 
 func (m *TaskComment) BeforeCreate(*gorm.DB) error { m.ensureID(); return nil }
 
+// MailNote is a project's SHARED memo on one client-domain email — any project
+// member can edit it (협업 메모). Keyed by (project, RFC822 Message-ID).
+type MailNote struct {
+	Base
+	ProjectID    string    `gorm:"index:idx_mailnote_pm,unique" json:"projectId"`
+	MessageID    string    `gorm:"index:idx_mailnote_pm,unique" json:"messageId"`
+	Body         string    `json:"body"`
+	LastEditedBy string    `json:"lastEditedBy"`
+	CreatedAt    time.Time `json:"createdAt"`
+	UpdatedAt    time.Time `json:"updatedAt"`
+}
+
+func (m *MailNote) BeforeCreate(*gorm.DB) error { m.ensureID(); return nil }
+
 // Contract holds the [admin-only] commercial terms of a project. BE is the
 // break-even floor (손해가 안 나는 최소 금액). Exposed ONLY to admins.
 type Contract struct {