diff --git a/components/settings/keyword-settings.tsx b/components/settings/keyword-settings.tsx
index e9b27827..5c11b989 100644
--- a/components/settings/keyword-settings.tsx
+++ b/components/settings/keyword-settings.tsx
@@ -3,8 +3,10 @@
 import { useState } from "react";
 import { useTranslations } from "next-intl";
 import { useSettingsStore, KEYWORD_PALETTE, DEFAULT_KEYWORDS, type KeywordDefinition } from "@/stores/settings-store";
+import { useAuthStore } from "@/stores/auth-store";
+import { useEmailStore } from "@/stores/email-store";
 import { SettingsSection } from "./settings-section";
-import { Plus, Pencil, Trash2, GripVertical, Check, X, RotateCcw } from "lucide-react";
+import { Plus, Pencil, Trash2, GripVertical, Check, X, RotateCcw, Loader2 } from "lucide-react";
 import { cn } from "@/lib/utils";
 
 const PALETTE_KEYS = Object.keys(KEYWORD_PALETTE);
@@ -91,16 +93,14 @@ function KeywordEditForm({
   const [color, setColor] = useState(initial?.color || "blue");
   const isEditing = !!initial;
 
-  const normalizedId = isEditing
-    ? initial.id
-    : label
-        .trim()
-        .toLowerCase()
-        .replace(/[^a-z0-9_-]/g, "-")
-        .replace(/-+/g, "-")
-        .replace(/^-|-$/g, "");
+  const normalizedId = label
+    .trim()
+    .toLowerCase()
+    .replace(/[^a-z0-9_-]/g, "-")
+    .replace(/-+/g, "-")
+    .replace(/^-|-$/g, "");
 
-  const isDuplicate = !isEditing && normalizedId.length > 0 && existingIds.includes(normalizedId);
+  const isDuplicate = normalizedId.length > 0 && existingIds.includes(normalizedId);
   const isValid = normalizedId.length > 0 && label.trim().length > 0 && !isDuplicate;
 
   const handleSave = () => {
@@ -159,10 +159,13 @@ function KeywordEditForm({
 
 export function KeywordSettings() {
   const t = useTranslations("settings.keywords");
-  const { emailKeywords, addKeyword, updateKeyword, removeKeyword, reorderKeywords } =
+  const { emailKeywords, addKeyword, updateKeyword, renameKeyword, removeKeyword, reorderKeywords } =
     useSettingsStore();
+  const { client } = useAuthStore();
+  const { fetchTagCounts } = useEmailStore();
   const [editingId, setEditingId] = useState<string | null>(null);
   const [isAdding, setIsAdding] = useState(false);
+  const [isMigrating, setIsMigrating] = useState(false);
 
   const existingIds = emailKeywords.map((k) => k.id);
 
@@ -171,8 +174,32 @@ export function KeywordSettings() {
     setIsAdding(false);
   };
 
-  const handleEdit = (keyword: KeywordDefinition) => {
-    updateKeyword(keyword.id, { label: keyword.label, color: keyword.color });
+  const handleEdit = async (keyword: KeywordDefinition) => {
+    const oldId = editingId;
+    if (!oldId) return;
+
+    const idChanged = oldId !== keyword.id;
+
+    if (idChanged && client) {
+      setIsMigrating(true);
+      try {
+        const oldJmapKeyword = `$label:${oldId}`;
+        const newJmapKeyword = `$label:${keyword.id}`;
+        await client.migrateKeyword(oldJmapKeyword, newJmapKeyword);
+        renameKeyword(oldId, keyword);
+        fetchTagCounts(client);
+      } catch (error) {
+        console.error("Failed to migrate keyword:", error);
+        const toastModule = await import('sonner');
+        toastModule.toast.error(t("migration_error"));
+        setIsMigrating(false);
+        return;
+      }
+      setIsMigrating(false);
+    } else {
+      updateKeyword(oldId, { label: keyword.label, color: keyword.color });
+    }
+
     setEditingId(null);
   };
 
@@ -187,6 +214,12 @@ export function KeywordSettings() {
   return (
     <SettingsSection title={t("title")} description={t("description")}>
       <div className="space-y-2">
+        {isMigrating && (
+          <div className="flex items-center gap-2 p-2 text-xs text-muted-foreground bg-accent/50 rounded-md">
+            <Loader2 className="w-3.5 h-3.5 animate-spin" />
+            {t("migrating")}
+          </div>
+        )}
         {emailKeywords.map((keyword) =>
           editingId === keyword.id ? (
             <KeywordEditForm
diff --git a/lib/demo/demo-client.ts b/lib/demo/demo-client.ts
index 2a8a6bcb..c8d92651 100644
--- a/lib/demo/demo-client.ts
+++ b/lib/demo/demo-client.ts
@@ -216,6 +216,18 @@ export class DemoJMAPClient implements IJMAPClient {
     if (email) email.keywords = { ...email.keywords, ...keywords };
   }
 
+  async migrateKeyword(oldKeyword: string, newKeyword: string): Promise<number> {
+    let count = 0;
+    for (const email of this.data.emails) {
+      if (email.keywords[oldKeyword]) {
+        delete email.keywords[oldKeyword];
+        email.keywords[newKeyword] = true;
+        count++;
+      }
+    }
+    return count;
+  }
+
   async deleteEmail(emailId: string): Promise<void> {
     this.data.emails = this.data.emails.filter(e => e.id !== emailId);
     this.recalcMailboxCounts();
diff --git a/lib/jmap/client-interface.ts b/lib/jmap/client-interface.ts
index 3717284e..ac529f27 100644
--- a/lib/jmap/client-interface.ts
+++ b/lib/jmap/client-interface.ts
@@ -72,6 +72,7 @@ export interface IJMAPClient {
   batchMarkAsRead(emailIds: string[], read?: boolean): Promise<void>;
   toggleStar(emailId: string, starred: boolean): Promise<void>;
   updateEmailKeywords(emailId: string, keywords: Record<string, boolean>): Promise<void>;
+  migrateKeyword(oldKeyword: string, newKeyword: string): Promise<number>;
   deleteEmail(emailId: string): Promise<void>;
   moveToTrash(emailId: string, trashMailboxId: string, accountId?: string): Promise<void>;
   batchDeleteEmails(emailIds: string[]): Promise<void>;
diff --git a/lib/jmap/client.ts b/lib/jmap/client.ts
index 0df69d63..cbef02cd 100644
--- a/lib/jmap/client.ts
+++ b/lib/jmap/client.ts
@@ -763,6 +763,56 @@ export class JMAPClient implements IJMAPClient {
     ]);
   }
 
+  async migrateKeyword(oldKeyword: string, newKeyword: string): Promise<number> {
+    // Query all email IDs that have the old keyword
+    const allIds: string[] = [];
+    let position = 0;
+    const batchSize = 100;
+
+    // eslint-disable-next-line no-constant-condition
+    while (true) {
+      const response = await this.request([
+        ["Email/query", {
+          accountId: this.accountId,
+          filter: { hasKeyword: oldKeyword },
+          limit: batchSize,
+          position,
+        }, "0"],
+      ]);
+
+      const queryResult = response.methodResponses?.[0]?.[1];
+      const ids: string[] = queryResult?.ids || [];
+      allIds.push(...ids);
+
+      if (ids.length < batchSize) break;
+      position += ids.length;
+    }
+
+    if (allIds.length === 0) return 0;
+
+    // Batch update: remove old keyword, add new keyword using per-property patches
+    const updateBatchSize = 50;
+    for (let i = 0; i < allIds.length; i += updateBatchSize) {
+      const batch = allIds.slice(i, i + updateBatchSize);
+      const update: Record<string, Record<string, boolean | null>> = {};
+      for (const id of batch) {
+        update[id] = {
+          [`keywords/${oldKeyword}`]: null,
+          [`keywords/${newKeyword}`]: true,
+        };
+      }
+
+      await this.request([
+        ["Email/set", {
+          accountId: this.accountId,
+          update,
+        }, "0"],
+      ]);
+    }
+
+    return allIds.length;
+  }
+
   async deleteEmail(emailId: string): Promise<void> {
     await this.request([
       ["Email/set", {
@@ -1359,34 +1409,35 @@ export class JMAPClient implements IJMAPClient {
       }));
     }
 
-    // Destroy old draft before creating replacement to avoid duplicates
-    const methodCalls: JMAPMethodCall[] = [];
+    // Use a single Email/set call with both destroy and create for atomicity
+    const setArgs: Record<string, unknown> = {
+      accountId: this.accountId,
+      create: { [emailId]: emailData },
+    };
     if (draftId) {
-      methodCalls.push(["Email/set", {
-        accountId: this.accountId, destroy: [draftId],
-      }, "0"]);
-      methodCalls.push(["Email/set", {
-        accountId: this.accountId, create: { [emailId]: emailData },
-      }, "1"]);
-    } else {
-      methodCalls.push(["Email/set", {
-        accountId: this.accountId, create: { [emailId]: emailData },
-      }, "0"]);
+      setArgs.destroy = [draftId];
     }
 
+    const methodCalls: JMAPMethodCall[] = [
+      ["Email/set", setArgs, "0"],
+    ];
+
     const response = await this.request(methodCalls);
-    const responseIndex = draftId ? 1 : 0;
 
-    if (response.methodResponses?.[responseIndex]?.[0] === "Email/set") {
-      const result = response.methodResponses[responseIndex][1];
+    if (response.methodResponses?.[0]?.[0] === "Email/set") {
+      const result = response.methodResponses[0][1];
 
-      if (result.notCreated || result.notUpdated) {
-        const errors = result.notCreated || result.notUpdated;
+      if (result.notCreated) {
+        const errors = result.notCreated;
         const firstError = Object.values(errors)[0] as { description?: string; type?: string };
         console.error('Draft save error:', firstError);
         throw new Error(firstError?.description || firstError?.type || 'Failed to save draft');
       }
 
+      if (draftId && result.notDestroyed) {
+        console.warn('Failed to destroy old draft:', result.notDestroyed);
+      }
+
       if (result.created?.[emailId]) {
         return result.created[emailId].id;
       }
diff --git a/locales/en/common.json b/locales/en/common.json
index 3c9698bd..0dc3243b 100644
--- a/locales/en/common.json
+++ b/locales/en/common.json
@@ -691,7 +691,9 @@
       "delete": "Delete keyword",
       "save": "Save",
       "add": "Add",
-      "cancel": "Cancel"
+      "cancel": "Cancel",
+      "migrating": "Updating keyword on existing emails…",
+      "migration_error": "Failed to update keyword on existing emails"
     },
     "language_region": {
       "title": "Language & Region",
diff --git a/stores/settings-store.ts b/stores/settings-store.ts
index ab4092a9..dfa4c802 100644
--- a/stores/settings-store.ts
+++ b/stores/settings-store.ts
@@ -157,6 +157,7 @@ interface SettingsState {
   // Keywords
   addKeyword: (keyword: KeywordDefinition) => void;
   updateKeyword: (id: string, updates: Partial<Omit<KeywordDefinition, 'id'>>) => void;
+  renameKeyword: (oldId: string, newKeyword: KeywordDefinition) => void;
   removeKeyword: (id: string) => void;
   reorderKeywords: (keywords: KeywordDefinition[]) => void;
   getKeywordById: (id: string) => KeywordDefinition | undefined;
@@ -389,6 +390,14 @@ export const useSettingsStore = create<SettingsState>()(
         });
       },
 
+      renameKeyword: (oldId: string, newKeyword: KeywordDefinition) => {
+        set({
+          emailKeywords: get().emailKeywords.map(k =>
+            k.id === oldId ? newKeyword : k
+          ),
+        });
+      },
+
       removeKeyword: (id: string) => {
         set({ emailKeywords: get().emailKeywords.filter(k => k.id !== id) });
       },