diff --git a/changelog.md b/changelog.md
index 8db1247..0fe6384 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## 2026-02-11 - 5.1.3 - fix(docs)
+clarify sendEmail default behavior and document automatic MX discovery and delivery modes
+
+- Updated README to describe automatic MX record discovery and grouping behavior when using sendEmail() (MTA mode)
+- Added a Delivery Modes section and API signature for sendEmail(mode) describing mta, forward, and process options
+- Expanded examples to show multi-recipient delivery, explicit mode usage, and retained low-level sendOutboundEmail example
+
 ## 2026-02-11 - 5.1.2 - fix(readme)
 adjust ASCII architecture diagram alignment in README
 
diff --git a/readme.md b/readme.md
index 4059031..7a5f5a2 100644
--- a/readme.md
+++ b/readme.md
@@ -1,6 +1,6 @@
 # @push.rocks/smartmta
 
-A high-performance, enterprise-grade Mail Transfer Agent (MTA) built from scratch in TypeScript with a Rust-powered SMTP engine — no nodemailer, no shortcuts. 🚀
+A high-performance, enterprise-grade Mail Transfer Agent (MTA) built from scratch in TypeScript with a Rust-powered SMTP engine — no nodemailer, no shortcuts. Automatic MX record discovery means you just call `sendEmail()` and smartmta figures out where to deliver. 🚀
 
 ## Issue Reporting and Security
 
@@ -78,9 +78,10 @@ After installation, run `pnpm build` to compile the Rust binary (`mailer-bin`).
 
 **Data flow for outbound mail:**
 
-1. 📝 TypeScript constructs the email and resolves DKIM keys for the sender domain
-2. 🦀 Sends to Rust via IPC — Rust builds the RFC 2822 message, signs with DKIM, and delivers via its SMTP client with connection pooling
-3. 📬 Result (accepted/rejected recipients, server response) returned to TypeScript
+1. 📝 TypeScript constructs the email and calls `sendEmail()` (defaults to MTA mode)
+2. 🔍 MTA mode automatically resolves MX records for each recipient domain, sorts by priority, and groups recipients for efficient delivery
+3. 🦀 Sends to Rust via IPC — Rust builds the RFC 2822 message, signs with DKIM, and delivers via its SMTP client with connection pooling
+4. 📬 Result (accepted/rejected recipients, server response) returned to TypeScript
 
 ## Usage
 
@@ -169,9 +170,9 @@ await emailServer.start();
 
 > 🔒 **Note:** `start()` will throw if the Rust binary is not compiled. Run `pnpm build` first.
 
-### 📧 Sending Outbound Emails
+### 📧 Sending Emails (Automatic MX Discovery)
 
-All outbound email delivery goes through the Rust SMTP client, accessed via `UnifiedEmailServer.sendOutboundEmail()`. The Rust client handles connection pooling, TLS negotiation, and DKIM signing automatically:
+The recommended way to send email is `sendEmail()`. It defaults to **MTA mode**, which automatically resolves MX records for each recipient domain via DNS — you don't need to know the destination mail server:
 
 ```typescript
 import { Email, UnifiedEmailServer } from '@push.rocks/smartmta';
@@ -179,8 +180,7 @@ import { Email, UnifiedEmailServer } from '@push.rocks/smartmta';
 // Build an email
 const email = new Email({
   from: 'sender@example.com',
-  to: ['recipient@example.com'],
-  cc: ['cc@example.com'],
+  to: ['alice@gmail.com', 'bob@company.org'],
   subject: 'Hello from smartmta! 🚀',
   text: 'Plain text body',
   html: '<h1>Hello!</h1><p>HTML body with <strong>formatting</strong></p>',
@@ -194,7 +194,50 @@ const email = new Email({
   ],
 });
 
-// Send via the Rust SMTP client (connection pooling, TLS, DKIM signing)
+// Send — MTA mode auto-discovers MX servers for gmail.com and company.org
+const emailId = await emailServer.sendEmail(email);
+
+// Optionally specify a delivery mode explicitly
+const emailId2 = await emailServer.sendEmail(email, 'mta');
+```
+
+In MTA mode, smartmta:
+- 🔍 Resolves MX records for each recipient domain (e.g. `gmail.com`, `company.org`)
+- 📊 Sorts MX hosts by priority (lowest = highest priority per RFC 5321)
+- 🔄 Tries each MX host in order until delivery succeeds
+- 🌐 Falls back to the domain's A record if no MX records exist
+- 📦 Groups recipients by domain for efficient batch delivery
+- 🔑 Signs outbound mail with DKIM automatically
+
+### 📮 Delivery Modes
+
+`sendEmail()` accepts a mode parameter that controls how the email is delivered:
+
+```typescript
+public async sendEmail(
+  email: Email,
+  mode: EmailProcessingMode = 'mta',  // 'mta' | 'forward' | 'process'
+  route?: IEmailRoute,
+  options?: {
+    skipSuppressionCheck?: boolean;
+    ipAddress?: string;
+    isTransactional?: boolean;
+  }
+): Promise<string>
+```
+
+| Mode | Description |
+|---|---|
+| `mta` (default) | **Auto MX discovery** — resolves MX records via DNS, delivers directly to the recipient's mail server. No relay configuration needed. |
+| `forward` | **Relay delivery** — forwards the email to a configured SMTP host (e.g. an internal mail gateway or third-party relay). |
+| `process` | **Scan + deliver** — runs the content scanning / security pipeline first, then delivers via auto MX resolution. |
+
+### 📬 Direct SMTP Delivery (Low-Level)
+
+For cases where you know the exact target SMTP server (e.g. relaying to a specific host), use the lower-level `sendOutboundEmail()`:
+
+```typescript
+// Send directly to a known SMTP server (bypasses MX resolution)
 const result = await emailServer.sendOutboundEmail('smtp.example.com', 587, email, {
   auth: { user: 'sender@example.com', pass: 'your-password' },
   dkimDomain: 'example.com',
diff --git a/ts/00_commitinfo_data.ts b/ts/00_commitinfo_data.ts
index 38df9c9..b5fb2f3 100644
--- a/ts/00_commitinfo_data.ts
+++ b/ts/00_commitinfo_data.ts
@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/smartmta',
-  version: '5.1.2',
+  version: '5.1.3',
   description: 'A high-performance, enterprise-grade Mail Transfer Agent (MTA) built from scratch in TypeScript with Rust acceleration.'
 }