Added more explicit type for SMTP config and refactored transport initialization.

server/mail/index.ts

@@ -0,0 +1,29 @@
+import {createTransport, Transporter} from "nodemailer";
+import {config} from "../config";
+import * as MailTemplateService from "../services/mailTemplateService";
+import Mail from "nodemailer/lib/mailer";
+import SMTPTransport from "nodemailer/lib/smtp-transport";
+
+let transporterSingleton: Transporter | null = null;
+
+function transporter() {
+    if (!transporterSingleton) {
+        const options = {
+            ...config.server.email.smtp,
+            pool: true,
+        };
+        transporterSingleton = createTransport(new SMTPTransport(options));
+
+        MailTemplateService.configureTransporter(transporterSingleton);
+    }
+
+    return transporterSingleton;
+}
+
+export function init(): void {
+    transporter();
+}
+
+export async function send(options: Mail.Options): Promise<void> {
+    await transporter().sendMail(options);
+}