feat(email): replace nodemailer with Resend for email delivery

Remove complex SMTP configuration and IPv4 workarounds by switching to the
Resend email API. This simplifies the email service, reduces dependencies,
and eliminates DNS-related connection issues. The global IPv4-first DNS
setting is no longer needed and has been removed from main.ts.

package-lock.json

@@ -31,6 +31,7 @@
         "passport": "^0.7.0",
         "passport-jwt": "^4.0.1",
         "pg": "^8.16.3",
+        "resend": "^6.12.0",
         "swagger-ui-express": "^5.0.1"
       },
       "devDependencies": {
@@ -1487,6 +1488,12 @@
       "hasInstallScript": true,
       "license": "Apache-2.0"
     },
+    "node_modules/@stablelib/base64": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/@stablelib/base64/-/base64-1.0.1.tgz",
+      "integrity": "sha512-1bnPQqSxSuc3Ii6MhBysoWCg58j97aUjuCSZrGSmDxNqtytIi0k8utUenAwTZN4V5mXXYGsVUI9zeBqy+jBOSQ==",
+      "license": "MIT"
+    },
     "node_modules/@standard-schema/spec": {
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/@standard-schema/spec/-/spec-1.1.0.tgz",
@@ -3493,6 +3500,12 @@
       "integrity": "sha512-W+KJc2dmILlPplD/H4K9l9LcAHAfPtP6BY84uVLXQ6Evcz9Lcg33Y2z1IVblT6xdY54PXYVHEv+0Wpq8Io6zkA==",
       "license": "MIT"
     },
+    "node_modules/fast-sha256": {
+      "version": "1.3.0",
+      "resolved": "https://registry.npmjs.org/fast-sha256/-/fast-sha256-1.3.0.tgz",
+      "integrity": "sha512-n11RGP/lrWEFI/bWdygLxhI+pVeo1ZYIVwvvPkW7azl/rOy+F3HYRZ2K5zeE9mmkhQppyv9sQFx0JM9UabnpPQ==",
+      "license": "Unlicense"
+    },
     "node_modules/fast-uri": {
       "version": "3.1.0",
       "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.0.tgz",
@@ -5134,6 +5147,12 @@
         "node": ">=4"
       }
     },
+    "node_modules/postal-mime": {
+      "version": "2.7.4",
+      "resolved": "https://registry.npmjs.org/postal-mime/-/postal-mime-2.7.4.tgz",
+      "integrity": "sha512-0WdnFQYUrPGGTFu1uOqD2s7omwua8xaeYGdO6rb88oD5yJ/4pPHDA4sdWqfD8wQVfCny563n/HQS7zTFft+f/g==",
+      "license": "MIT-0"
+    },
     "node_modules/postgres": {
       "version": "3.4.7",
       "resolved": "https://registry.npmjs.org/postgres/-/postgres-3.4.7.tgz",
@@ -5471,6 +5490,27 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/resend": {
+      "version": "6.12.0",
+      "resolved": "https://registry.npmjs.org/resend/-/resend-6.12.0.tgz",
+      "integrity": "sha512-CaxEvX1z+/MGbgnhsM/bvmkbnZd1v1sEXELAjBNSDBQNMaB7MgqOyrBgI27CYikEgdaDnBrXghAXYWTBs/h5Bw==",
+      "license": "MIT",
+      "dependencies": {
+        "postal-mime": "2.7.4",
+        "svix": "1.90.0"
+      },
+      "engines": {
+        "node": ">=20"
+      },
+      "peerDependencies": {
+        "@react-email/render": "*"
+      },
+      "peerDependenciesMeta": {
+        "@react-email/render": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/resolve-from": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/resolve-from/-/resolve-from-4.0.0.tgz",
@@ -5907,6 +5947,16 @@
         "node": ">= 0.6"
       }
     },
+    "node_modules/standardwebhooks": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/standardwebhooks/-/standardwebhooks-1.0.0.tgz",
+      "integrity": "sha512-BbHGOQK9olHPMvQNHWul6MYlrRTAOKn03rOe4A8O3CLWhNf4YHBqq2HJKKC+sfqpxiBY52pNeesD6jIiLDz8jg==",
+      "license": "MIT",
+      "dependencies": {
+        "@stablelib/base64": "^1.0.0",
+        "fast-sha256": "^1.3.0"
+      }
+    },
     "node_modules/statuses": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/statuses/-/statuses-2.0.2.tgz",
@@ -6016,6 +6066,16 @@
         "node": ">=8"
       }
     },
+    "node_modules/svix": {
+      "version": "1.90.0",
+      "resolved": "https://registry.npmjs.org/svix/-/svix-1.90.0.tgz",
+      "integrity": "sha512-ljkZuyy2+IBEoESkIpn8sLM+sxJHQcPxlZFxU+nVDhltNfUMisMBzWX/UR8SjEnzoI28ZjCzMbmYAPwSTucoMw==",
+      "license": "MIT",
+      "dependencies": {
+        "standardwebhooks": "1.0.0",
+        "uuid": "^10.0.0"
+      }
+    },
     "node_modules/swagger-ui-dist": {
       "version": "5.31.0",
       "resolved": "https://registry.npmjs.org/swagger-ui-dist/-/swagger-ui-dist-5.31.0.tgz",
@@ -6513,6 +6573,19 @@
         "node": ">= 0.4.0"
       }
     },
+    "node_modules/uuid": {
+      "version": "10.0.0",
+      "resolved": "https://registry.npmjs.org/uuid/-/uuid-10.0.0.tgz",
+      "integrity": "sha512-8XkAphELsDnEGrDxUOHB3RGvXz6TeuYSGEZBOjtTtPm2lwhGBjLgOzLHB63IUWfBpNucQjND6d3AOudO+H3RWQ==",
+      "funding": [
+        "https://github.com/sponsors/broofa",
+        "https://github.com/sponsors/ctavan"
+      ],
+      "license": "MIT",
+      "bin": {
+        "uuid": "dist/bin/uuid"
+      }
+    },
     "node_modules/v8-compile-cache-lib": {
       "version": "3.0.1",
       "resolved": "https://registry.npmjs.org/v8-compile-cache-lib/-/v8-compile-cache-lib-3.0.1.tgz",

package.json

@@ -70,6 +70,7 @@
     "passport": "^0.7.0",
     "passport-jwt": "^4.0.1",
     "pg": "^8.16.3",
+    "resend": "^6.12.0",
     "swagger-ui-express": "^5.0.1"
   }
 }

src/main.ts

@@ -1,9 +1,3 @@
-// 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";

src/notifications/email.service.ts

@@ -1,48 +1,24 @@
 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");
+import { Resend } from "resend";
 
 @Injectable()
 export class EmailService {
   private readonly logger = new Logger(EmailService.name);
-  private transporter: nodemailer.Transporter;
+  private readonly resend: Resend;
+  private readonly fromAddress: string;
 
   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";
+    const apiKey = this.configService.get<string>("RESEND_API_KEY");
+
+    if (!apiKey) {
+      this.logger.error("RESEND_API_KEY is not set. Emails will not be sent.");
+    }
 
-    this.transporter = nodemailer.createTransport({
-      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<string>("SMTP_USER"),
-        pass: this.configService.get<string>("SMTP_PASS"),
-      },
-      tls: {
-        // Must match the real hostname for SNI even if we resolve the IP manually
-        servername: smtpHost,
-        rejectUnauthorized: false,
-      },
-    } as any);
+    this.resend = new Resend(apiKey);
+    this.fromAddress =
+      this.configService.get<string>("SMTP_FROM") ||
+      "MaternAlert <onboarding@resend.dev>";
   }
 
   async sendEmail(
@@ -51,36 +27,28 @@ export class EmailService {
     text: string,
     html?: string,
   ): Promise<boolean> {
-    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));
-        }
+    try {
+      const { data, error } = await this.resend.emails.send({
+        from: this.fromAddress,
+        to,
+        subject,
+        text,
+        html: html || text,
+      });
+
+      if (error) {
+        this.logger.error(`Failed to send email to ${to}: ${error.message}`);
+        return false;
       }
-    }
 
-    return false;
+      this.logger.log(`Email sent successfully: ${data?.id} to ${to}`);
+      return true;
+    } catch (error: any) {
+      this.logger.error(
+        `Unexpected error sending email to ${to}: ${error.message}`,
+        error.stack,
+      );
+      return false;
+    }
   }
 }