diff --git a/domain/user-repository.js b/domain/user-repository.js
index 21598d4..83aafe9 100644
--- a/domain/user-repository.js
+++ b/domain/user-repository.js
@@ -33,7 +33,7 @@ class UserRepository {
             debug(`Connected to user database: ${this.dbPath}`)
 
             // Load and execute schema
-            const schemaPath = path.join(__dirname, '../db/schema.sql')
+            const schemaPath = path.join(__dirname, '../schema.sql')
             const schema = fs.readFileSync(schemaPath, 'utf8')
             this.db.exec(schema)
             debug('Database schema initialized')
diff --git a/schema.sql b/schema.sql
new file mode 100644
index 0000000..a30b2a5
--- /dev/null
+++ b/schema.sql
@@ -0,0 +1,53 @@
+-- User Registration System Schema
+-- SQLite database for user accounts and associated features
+
+-- Users table
+CREATE TABLE IF NOT EXISTS users (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    username TEXT UNIQUE NOT NULL COLLATE NOCASE,
+    password_hash TEXT NOT NULL,
+    created_at INTEGER NOT NULL,
+    last_login INTEGER,
+    CHECK (length(username) >= 3 AND length(username) <= 20)
+);
+
+CREATE INDEX IF NOT EXISTS idx_users_username ON users(username);
+CREATE INDEX IF NOT EXISTS idx_users_created_at ON users(created_at);
+
+-- User verified forwarding emails
+CREATE TABLE IF NOT EXISTS user_forward_emails (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id INTEGER NOT NULL,
+    email TEXT NOT NULL COLLATE NOCASE,
+    verified_at INTEGER NOT NULL,
+    created_at INTEGER NOT NULL,
+    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
+    UNIQUE(user_id, email)
+);
+
+CREATE INDEX IF NOT EXISTS idx_forward_emails_user_id ON user_forward_emails(user_id);
+CREATE INDEX IF NOT EXISTS idx_forward_emails_email ON user_forward_emails(email);
+
+-- User locked inboxes
+CREATE TABLE IF NOT EXISTS user_locked_inboxes (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id INTEGER NOT NULL,
+    inbox_address TEXT NOT NULL COLLATE NOCASE,
+    password_hash TEXT NOT NULL,
+    locked_at INTEGER NOT NULL,
+    last_accessed INTEGER NOT NULL,
+    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
+    UNIQUE(user_id, inbox_address)
+);
+
+CREATE INDEX IF NOT EXISTS idx_locked_inboxes_user_id ON user_locked_inboxes(user_id);
+CREATE INDEX IF NOT EXISTS idx_locked_inboxes_address ON user_locked_inboxes(inbox_address);
+CREATE INDEX IF NOT EXISTS idx_locked_inboxes_last_accessed ON user_locked_inboxes(last_accessed);
+
+-- Trigger to enforce max 5 locked inboxes per user
+CREATE TRIGGER IF NOT EXISTS check_locked_inbox_limit
+BEFORE INSERT ON user_locked_inboxes
+BEGIN
+    SELECT RAISE(ABORT, 'User already has maximum number of locked inboxes')
+    WHERE (SELECT COUNT(*) FROM user_locked_inboxes WHERE user_id = NEW.user_id) >= 5;
+END;