diff --git a/js/mzta-storage.js b/js/mzta-storage.js
new file mode 100644
index 00000000..21ceb5b7
--- /dev/null
+++ b/js/mzta-storage.js
@@ -0,0 +1,187 @@
+/*
+ *  ThunderAI [https://micz.it/thunderbird-addon-thunderai/]
+ *  Copyright (C) 2024 - 2026  Mic (m@micz.it)
+
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import { taLogger } from './mzta-logger.js';
+
+export class taStorage {
+
+    static STORAGE_KEY_PREFIX = 'msg:';
+    static SCHEMA_VERSION = 1;
+
+    logger = null;
+
+    constructor(do_debug = false) {
+        this.taLog = new taLogger("mzta-storage", do_debug);
+    }
+
+    /**
+     * Build the storage key for a given Message-ID.
+     * @param {string} messageId - The Message-ID header string.
+     * @returns {string} The prefixed storage key.
+     */
+    _buildKey(messageId) {
+        return taStorage.STORAGE_KEY_PREFIX + messageId;
+    }
+
+    /**
+     * Read the full record for a given Message-ID.
+     * @param {string} messageId - The Message-ID header string.
+     * @returns {Promise<object|null>} The record object or null if not found.
+     */
+    async getRecord(messageId) {
+        try {
+            let key = this._buildKey(messageId);
+            let result = await messenger.storage.local.get(key);
+            return result[key] || null;
+        } catch (e) {
+            this.taLog.error('getRecord error: ' + e);
+            return null;
+        }
+    }
+
+    /**
+     * Check if a record exists and contains the specified field.
+     * @param {string} messageId - The Message-ID header string.
+     * @param {string} field - The field name to check ("spam", "summary", or "translation").
+     * @returns {Promise<boolean>} True if the record exists and the field is present.
+     */
+    async hasField(messageId, field) {
+        try {
+            let record = await this.getRecord(messageId);
+            return record !== null && field in record;
+        } catch (e) {
+            this.taLog.error('hasField error: ' + e);
+            return false;
+        }
+    }
+
+    /**
+     * Write the spam field for a given Message-ID.
+     * @param {string} messageId - The Message-ID header string.
+     * @param {number} score - Spam score (float 0-1).
+     * @param {string} reason - Textual motivation for the score.
+     * @param {boolean} [force=false] - If true, overwrite existing spam data.
+     */
+    async writeSpam(messageId, score, reason, force = true) {
+        try {
+            let key = this._buildKey(messageId);
+            let record = await this.getRecord(messageId) || { v: taStorage.SCHEMA_VERSION };
+            if ('spam' in record && !force) {
+                return;
+            }
+            let now = Date.now();
+            record.spam = { score: score, reason: reason, ts: now };
+            record.ts = now;
+            await messenger.storage.local.set({ [key]: record });
+        } catch (e) {
+            this.taLog.error('writeSpam error: ' + e);
+        }
+    }
+
+    /**
+     * Write the summary field for a given Message-ID.
+     * @param {string} messageId - The Message-ID header string.
+     * @param {string} text - The summary text.
+     * @param {string} lang - The language of the summary.
+     * @param {boolean} [force=false] - If true, overwrite existing summary data.
+     */
+    async writeSummary(messageId, text, force = true) {
+        try {
+            let key = this._buildKey(messageId);
+            let record = await this.getRecord(messageId) || { v: taStorage.SCHEMA_VERSION };
+            if ('summary' in record && !force) {
+                return;
+            }
+            let now = Date.now();
+            record.summary = { text: text, ts: now };
+            record.ts = now;
+            await messenger.storage.local.set({ [key]: record });
+        } catch (e) {
+            this.taLog.error('writeSummary error: ' + e);
+        }
+    }
+
+    /**
+     * Write the translation field for a given Message-ID.
+     * @param {string} messageId - The Message-ID header string.
+     * @param {string} from - Source language code.
+     * @param {string} to - Target language code.
+     * @param {string} text - The translated text.
+     * @param {boolean} [force=false] - If true, overwrite existing translation data.
+     */
+    async writeTranslation(messageId, translated_text, lang, force = true) {
+        try {
+            let key = this._buildKey(messageId);
+            let record = await this.getRecord(messageId) || { v: taStorage.SCHEMA_VERSION };
+            if ('translation' in record && !force) {
+                return;
+            }
+            let now = Date.now();
+            record.translation = { translated_text: translated_text, lang: lang, ts: now };
+            record.ts = now;
+            await messenger.storage.local.set({ [key]: record });
+        } catch (e) {
+            this.taLog.error('writeTranslation error: ' + e);
+        }
+    }
+
+    /**
+     * Delete the entire record for a given Message-ID.
+     * @param {string} messageId - The Message-ID header string.
+     */
+    async deleteRecord(messageId) {
+        try {
+            let key = this._buildKey(messageId);
+            await messenger.storage.local.remove(key);
+        } catch (e) {
+            this.taLog.error('deleteRecord error: ' + e);
+        }
+    }
+
+    /**
+     * Remove all records older than maxAgeDays.
+     * @param {number} maxAgeDays - Maximum age in days. If 0, does nothing.
+     * @returns {Promise<number>} The number of deleted records.
+     */
+    async cleanup(maxAgeDays) {
+        if (maxAgeDays === 0) {
+            return 0;
+        }
+        try {
+            let all = await messenger.storage.local.get(null);
+            let cutoff = Date.now() - (maxAgeDays * 24 * 60 * 60 * 1000);
+            let keysToDelete = [];
+            for (let key of Object.keys(all)) {
+                if (!key.startsWith(taStorage.STORAGE_KEY_PREFIX)) {
+                    continue;
+                }
+                let record = all[key];
+                if (record.ts && record.ts < cutoff) {
+                    keysToDelete.push(key);
+                }
+            }
+            if (keysToDelete.length > 0) {
+                await messenger.storage.local.remove(keysToDelete);
+            }
+            return keysToDelete.length;
+        } catch (e) {
+            this.taLog.error('cleanup error: ' + e);
+            return 0;
+        }
+    }
+}