nodemailer: MimeNode.build returns Promise (#41068)

* nodemailer: MimeNode.build returns Promise

* nodemailer: definition for v6.4

types/nodemailer/index.d.ts

@@ -1,4 +1,4 @@
-// Type definitions for Nodemailer 6.2
+// Type definitions for Nodemailer 6.4
 // Project: https://github.com/nodemailer/nodemailer, https://nodemailer.com
 // Definitions by: Rogier Schouten <https://github.com/rogierschouten>
 //                 Piotr Roszatycki <https://github.com/dex4er>

types/nodemailer/lib/mime-node/index.d.ts

@@ -87,8 +87,9 @@ declare class MimeNode {
      */
     setContent(content: string | Buffer | Readable): this;
 
-    /** Generate the message and return it with a callback */
+    /** Generate the message and return it with a callback or promise */
     build(callback: (err: Error | null, buf: Buffer) => void): void;
+    build(): Promise<Buffer>;
 
     getTransferEncoding(): string;
 

types/nodemailer/nodemailer-tests.ts

@@ -1282,13 +1282,19 @@ function mailcomposer_createReadStream_test() {
 
 // build
 
-function mailcomposer_build_test() {
+function mailcomposer_build_callback_test() {
     const mail = new MailComposer({ from: '...' });
     mail.compile().build((err, message) => {
         process.stdout.write(message);
     });
 }
 
+async function mailcomposer_build_promise_test() {
+    const mail = new MailComposer({ from: '...' });
+    const message = await mail.compile().build();
+    process.stdout.write(message);
+}
+
 // addressparser
 
 function isAddress(addressOrGroup: addressparser.AddressOrGroup): addressOrGroup is addressparser.Address {