fix: Support Exchange servers without authentication

- Make email authentication optional in transporter config
- Only add auth object if both username and password are provided
- Update initialization to only require SMTP_HOST
- Add logging to show whether auth is enabled
- Update documentation with no-auth configuration examples
- Fix "Unrecognized authentication type" error for open relays

Exchange servers configured as internal relays often don't
require authentication. This fix allows using them by leaving
SMTP_USER and SMTP_PASS empty in the .env file.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/src/services/report.service.js

@@ -10,23 +10,19 @@ class ReportService {
     this.transporter = null;
     this.scheduledTask = null;
     
-    if (config.email.host && config.email.auth.user) {
+    if (config.email.host) {
       this.initializeMailer();
       this.setupSchedule();
     } else {
-      logger.warn('Email configuration missing. Report scheduling disabled.');
+      logger.warn('Email host not configured. Report scheduling disabled.');
     }
   }
 
   initializeMailer() {
-    this.transporter = nodemailer.createTransport({
+    const transportConfig = {
       host: config.email.host,
       port: config.email.port,
       secure: config.email.secure,
-      auth: {
-        user: config.email.auth.user,
-        pass: config.email.auth.pass,
-      },
       // For Exchange Server on port 25 without TLS
       tls: {
         rejectUnauthorized: false, // Accept self-signed certificates
@@ -36,7 +32,20 @@ class ReportService {
       // Disable STARTTLS for port 25 if not using secure
       requireTLS: config.email.secure,
       ignoreTLS: config.email.port === 25 && !config.email.secure,
-    });
+    };
+
+    // Only add auth if username and password are provided
+    if (config.email.auth.user && config.email.auth.pass) {
+      transportConfig.auth = {
+        user: config.email.auth.user,
+        pass: config.email.auth.pass,
+      };
+      logger.info('Email configured with authentication');
+    } else {
+      logger.info('Email configured without authentication (open relay)');
+    }
+
+    this.transporter = nodemailer.createTransport(transportConfig);
 
     // Verify connection
     this.transporter.verify((error) => {