diff --git a/app/api/extension-requests/[id]/route.ts b/app/api/extension-requests/[id]/route.ts
index c54c344..c26776d 100644
--- a/app/api/extension-requests/[id]/route.ts
+++ b/app/api/extension-requests/[id]/route.ts
@@ -40,12 +40,12 @@ export const PATCH = withApiHandler<{ id: string }>(
         id: maestroExtensionID,
         duration: Date.now() - t0,
       });
-      void sendExtensionDoneEmail(
+      const emailSent = await sendExtensionDoneEmail(
         result.maestroName,
         result.maestroEmail,
         formatDate(result.availableActivateDateTime)
       );
-      return NextResponse.json({ ok: true, availableActivateDateTime: result.availableActivateDateTime });
+      return NextResponse.json({ ok: true, availableActivateDateTime: result.availableActivateDateTime, emailSent });
     }
 
     await cancelExtensionRequest(maestroExtensionID);
diff --git a/app/api/upgrade-requests/[id]/route.ts b/app/api/upgrade-requests/[id]/route.ts
index a445da6..7cc0bcf 100644
--- a/app/api/upgrade-requests/[id]/route.ts
+++ b/app/api/upgrade-requests/[id]/route.ts
@@ -40,7 +40,7 @@ export const PATCH = withApiHandler<{ id: string }>(
         id: maestroUpgradeID,
         duration: Date.now() - t0,
       });
-      void sendUpgradeDoneEmail(
+      const emailSent = await sendUpgradeDoneEmail(
         result.maestroName,
         result.maestroEmail,
         result.registeredActivateStatus,
@@ -48,7 +48,7 @@ export const PATCH = withApiHandler<{ id: string }>(
         result.requestedAccountType,
         formatDate(result.availableActivateDateTime)
       );
-      return NextResponse.json({ ok: true, availableActivateDateTime: result.availableActivateDateTime });
+      return NextResponse.json({ ok: true, availableActivateDateTime: result.availableActivateDateTime, emailSent });
     }
 
     await rejectUpgradeRequest(maestroUpgradeID);
diff --git a/components/data-table/extension-requests-table.tsx b/components/data-table/extension-requests-table.tsx
index 2b4b483..2fa93f4 100644
--- a/components/data-table/extension-requests-table.tsx
+++ b/components/data-table/extension-requests-table.tsx
@@ -108,19 +108,16 @@ function ExtensionRequestActions({
   const router = useRouter();
   const [isPending, startTransition] = useTransition();
   const [errorMessage, setErrorMessage] = useState("");
+  const [emailWarning, setEmailWarning] = useState(false);
   const isRequested = request.status === REQUEST_STATUSES.REQUESTED;
 
-  if (!isRequested) {
+  if (!isRequested && !emailWarning) {
     return <span className="text-xs text-muted-foreground">처리 완료</span>;
   }
 
   async function submitAction(action: "approve" | "cancel") {
     const actionLabel = action === "approve" ? "승인" : "취소";
-    const confirmed = window.confirm(
-      `${request.maestroName} 연장 신청을 ${actionLabel}하시겠습니까?`
-    );
-
-    if (!confirmed) {
+    if (!window.confirm(`${request.maestroName} 연장 신청을 ${actionLabel}하시겠습니까?`)) {
       return;
     }
 
@@ -136,14 +133,19 @@ function ExtensionRequestActions({
         }
       );
 
-      if (!response.ok) {
-        const body = (await response.json().catch(() => null)) as {
-          message?: string;
-        } | null;
+      const body = (await response.json().catch(() => null)) as {
+        message?: string;
+        emailSent?: boolean;
+      } | null;
 
+      if (!response.ok) {
         throw new Error(body?.message ?? "연장 신청 처리에 실패했습니다.");
       }
 
+      if (action === "approve" && body?.emailSent === false) {
+        setEmailWarning(true);
+      }
+
       startTransition(() => {
         router.refresh();
       });
@@ -158,27 +160,36 @@ function ExtensionRequestActions({
 
   return (
     <div className="space-y-2">
-      <div className="flex items-center gap-2">
-        <Button
-          disabled={isPending}
-          onClick={() => void submitAction("approve")}
-          size="sm"
-          type="button"
-        >
-          <Check className="size-4" aria-hidden="true" />
-          승인
-        </Button>
-        <Button
-          disabled={isPending}
-          onClick={() => void submitAction("cancel")}
-          size="sm"
-          type="button"
-          variant="outline"
-        >
-          <X className="size-4" aria-hidden="true" />
-          취소
-        </Button>
-      </div>
+      {isRequested ? (
+        <div className="flex items-center gap-2">
+          <Button
+            disabled={isPending}
+            onClick={() => void submitAction("approve")}
+            size="sm"
+            type="button"
+          >
+            <Check className="size-4" aria-hidden="true" />
+            승인
+          </Button>
+          <Button
+            disabled={isPending}
+            onClick={() => void submitAction("cancel")}
+            size="sm"
+            type="button"
+            variant="outline"
+          >
+            <X className="size-4" aria-hidden="true" />
+            취소
+          </Button>
+        </div>
+      ) : (
+        <span className="text-xs text-muted-foreground">처리 완료</span>
+      )}
+      {emailWarning ? (
+        <p className="max-w-56 text-xs text-amber-600 dark:text-amber-400">
+          이메일 발송 실패 — 수동 확인 필요
+        </p>
+      ) : null}
       {errorMessage ? (
         <p className="max-w-56 text-xs text-destructive">{errorMessage}</p>
       ) : null}
diff --git a/components/data-table/upgrade-requests-table.tsx b/components/data-table/upgrade-requests-table.tsx
index 65d36c0..a0cb1df 100644
--- a/components/data-table/upgrade-requests-table.tsx
+++ b/components/data-table/upgrade-requests-table.tsx
@@ -113,19 +113,16 @@ function UpgradeRequestActions({
   const router = useRouter();
   const [isPending, startTransition] = useTransition();
   const [errorMessage, setErrorMessage] = useState("");
+  const [emailWarning, setEmailWarning] = useState(false);
   const isRequested = request.status === REQUEST_STATUSES.REQUESTED;
 
-  if (!isRequested) {
+  if (!isRequested && !emailWarning) {
     return <span className="text-xs text-muted-foreground">처리 완료</span>;
   }
 
   async function submitAction(action: "approve" | "reject") {
     const actionLabel = action === "approve" ? "승인" : "거절";
-    const confirmed = window.confirm(
-      `${request.maestroName} 업그레이드 신청을 ${actionLabel}하시겠습니까?`
-    );
-
-    if (!confirmed) {
+    if (!window.confirm(`${request.maestroName} 업그레이드 신청을 ${actionLabel}하시겠습니까?`)) {
       return;
     }
 
@@ -141,14 +138,17 @@ function UpgradeRequestActions({
         }
       );
 
-      if (!response.ok) {
-        const body = (await response.json().catch(() => null)) as {
-          message?: string;
-        } | null;
+      const body = (await response.json().catch(() => null)) as {
+        message?: string;
+        emailSent?: boolean;
+      } | null;
 
-        throw new Error(
-          body?.message ?? "업그레이드 신청 처리에 실패했습니다."
-        );
+      if (!response.ok) {
+        throw new Error(body?.message ?? "업그레이드 신청 처리에 실패했습니다.");
+      }
+
+      if (action === "approve" && body?.emailSent === false) {
+        setEmailWarning(true);
       }
 
       startTransition(() => {
@@ -165,27 +165,36 @@ function UpgradeRequestActions({
 
   return (
     <div className="space-y-2">
-      <div className="flex items-center gap-2">
-        <Button
-          disabled={isPending}
-          onClick={() => void submitAction("approve")}
-          size="sm"
-          type="button"
-        >
-          <Check className="size-4" aria-hidden="true" />
-          승인
-        </Button>
-        <Button
-          disabled={isPending}
-          onClick={() => void submitAction("reject")}
-          size="sm"
-          type="button"
-          variant="outline"
-        >
-          <X className="size-4" aria-hidden="true" />
-          거절
-        </Button>
-      </div>
+      {isRequested ? (
+        <div className="flex items-center gap-2">
+          <Button
+            disabled={isPending}
+            onClick={() => void submitAction("approve")}
+            size="sm"
+            type="button"
+          >
+            <Check className="size-4" aria-hidden="true" />
+            승인
+          </Button>
+          <Button
+            disabled={isPending}
+            onClick={() => void submitAction("reject")}
+            size="sm"
+            type="button"
+            variant="outline"
+          >
+            <X className="size-4" aria-hidden="true" />
+            거절
+          </Button>
+        </div>
+      ) : (
+        <span className="text-xs text-muted-foreground">처리 완료</span>
+      )}
+      {emailWarning ? (
+        <p className="max-w-56 text-xs text-amber-600 dark:text-amber-400">
+          이메일 발송 실패 — 수동 확인 필요
+        </p>
+      ) : null}
       {errorMessage ? (
         <p className="max-w-56 text-xs text-destructive">{errorMessage}</p>
       ) : null}
diff --git a/docs/plan/improvement-plan.md b/docs/plan/improvement-plan.md
index bd191ef..8b65aae 100644
--- a/docs/plan/improvement-plan.md
+++ b/docs/plan/improvement-plan.md
@@ -168,9 +168,10 @@
    - P1-5: `request_extension_maestro` / `request_upgrade_maestro` 로그 추가
    - P1-7: 관리자 대행 등록 시 입금 메일 미발송 — 의도 확인, AGENTS.md에 명시
    - P2-10: 신청 시점 스냅샷 유지 — 변경 없음
-3. **Step 3 (P1-6 이메일 + 검증)**
-   - emailSent 응답 + UI 경고, stage에서 연장/업그레이드(체험→유료, 유료→유료) 메일 실측
-     (phase11 잔여 항목 겸)
+3. **Step 3 (P1-6 이메일 + 검증) ✅ 완료 (2026-07-04)**
+   - API route 2곳: `void sendXxxDoneEmail` → `await emailSent`, 응답에 `emailSent: boolean` 포함
+   - 테이블 UI 2곳: 응답 body를 단일 파싱으로 통일, 승인 성공 후 `emailSent === false`이면 인라인 경고 표시 (`router.refresh()` 후에도 client state 유지됨)
+   - stage 실측(체험→유료, 유료→유료 메일 검증)은 별도 수동 테스트 항목으로 남김
 4. **Step 4 (P2 일괄)**
    - 소규모 항목 묶음 처리 후 AGENTS.md / phase 문서 갱신