fix(email): enforce IPv4 DNS resolution and add retry logic

Force IPv4-first DNS resolution globally and in email service to prevent
IPv6 connection failures with SMTP hosts like Gmail. Add retry logic with
2 attempts and shorter timeouts to improve email delivery reliability.

src/main.ts

@@ -1,3 +1,9 @@
+// Force IPv4-first DNS globally — must be the very first import to prevent
+// nodemailer (and any other net module) from attempting IPv6 connections on
+// hosts that don't support it (e.g. smtp.gmail.com port 587).
+import * as dns from "dns";
+dns.setDefaultResultOrder("ipv4first");
+
 import { NestFactory } from "@nestjs/core";
 import { AppModule } from "./app.module";
 import { setupGlobalMiddleware } from "./setup";
@@ -8,7 +14,7 @@ async function bootstrap() {
   setupGlobalMiddleware(app);
 
   const port = process.env.PORT || 3000;
-  await app.listen(port, '0.0.0.0');
+  await app.listen(port, "0.0.0.0");
 
   console.log(`\n🏥 Maternal Health Support Backend`);
   console.log(`⚠️  CARE-SUPPORT TOOL - NOT A DIAGNOSTIC SYSTEM`);

src/notifications/email.service.ts

@@ -1,6 +1,10 @@
 import { Injectable, Logger } from "@nestjs/common";
 import { ConfigService } from "@nestjs/config";
 import * as nodemailer from "nodemailer";
+import * as dns from "dns";
+
+// Force all DNS lookups in this process to prefer IPv4
+dns.setDefaultResultOrder("ipv4first");
 
 @Injectable()
 export class EmailService {
@@ -8,26 +12,35 @@ export class EmailService {
   private transporter: nodemailer.Transporter;
 
   constructor(private readonly configService: ConfigService) {
+    const smtpHost =
+      this.configService.get<string>("SMTP_HOST") || "smtp.gmail.com";
+    const smtpPort = parseInt(
+      this.configService.get<string>("SMTP_PORT") || "587",
+      10,
+    );
+    const smtpSecure = this.configService.get<string>("SMTP_SECURE") === "true";
+
     this.transporter = nodemailer.createTransport({
-      host: this.configService.get("SMTP_HOST"),
-      port: parseInt(this.configService.get("SMTP_PORT") || "587", 10),
-      secure: this.configService.get("SMTP_SECURE") === "true",
-      family: 4, // Force IPv4
-      pool: false, // Turn off pool to debug fresh connections
-
-      maxConnections: 5,
-      maxMessages: 100,
-      connectionTimeout: 20000,
-      greetingTimeout: 20000,
-      socketTimeout: 30000,
+      host: smtpHost,
+      port: smtpPort,
+      secure: smtpSecure,
+      // Explicitly force IPv4 — prevents nodemailer falling back to IPv6 after a
+      // timeout on the IPv4 address when the host resolves to both record types.
+      family: 4,
+      pool: false,
+      connectionTimeout: 15000,
+      greetingTimeout: 15000,
+      socketTimeout: 20000,
       debug: true,
       logger: true,
       auth: {
-        user: this.configService.get("SMTP_USER"),
-        pass: this.configService.get("SMTP_PASS"),
+        user: this.configService.get<string>("SMTP_USER"),
+        pass: this.configService.get<string>("SMTP_PASS"),
       },
       tls: {
-        rejectUnauthorized: false, // Help with some SMTP issues
+        // Must match the real hostname for SNI even if we resolve the IP manually
+        servername: smtpHost,
+        rejectUnauthorized: false,
       },
     } as any);
   }
@@ -38,25 +51,36 @@ export class EmailService {
     text: string,
     html?: string,
   ): Promise<boolean> {
-    try {
-      const from = this.configService.get("SMTP_FROM");
-
-      const info = await this.transporter.sendMail({
-        from,
-        to,
-        subject,
-        text,
-        html: html || text,
-      });
-
-      this.logger.log(`Email sent successfully: ${info.messageId} to ${to}`);
-      return true;
-    } catch (error: any) {
-      this.logger.error(
-        `Failed to send email to ${to}: ${error.message}`,
-        error.stack,
-      );
-      return false;
+    const from = this.configService.get<string>("SMTP_FROM");
+    const maxAttempts = 2;
+
+    for (let attempt = 1; attempt <= maxAttempts; attempt++) {
+      try {
+        const info = await this.transporter.sendMail({
+          from,
+          to,
+          subject,
+          text,
+          html: html || text,
+        });
+
+        this.logger.log(
+          `Email sent successfully (attempt ${attempt}): ${info.messageId} to ${to}`,
+        );
+        return true;
+      } catch (error: any) {
+        this.logger.error(
+          `Failed to send email to ${to} (attempt ${attempt}/${maxAttempts}): ${error.message}`,
+          attempt === maxAttempts ? error.stack : undefined,
+        );
+
+        if (attempt < maxAttempts) {
+          // Wait 2 s before retrying
+          await new Promise((resolve) => setTimeout(resolve, 2000));
+        }
+      }
     }
+
+    return false;
   }
 }