Allows multiple reply-to addresses

extensions/mailer/runtime/src/main/java/io/quarkus/mailer/Mail.java

@@ -17,7 +17,7 @@ public class Mail {
     private List<String> bcc = new ArrayList<>();
     private List<String> cc = new ArrayList<>();
     private String from;
-    private String replyTo;
+    private List<String> replyTo = new ArrayList<>();
     private String bounceAddress;
     private String subject;
     private String text;
@@ -163,20 +163,52 @@ public Mail setFrom(String from) {
     }
 
     /**
-     * @return the reply-to address.
+     * @return the reply-to address. In the case of multiple addresses, the comma-separated list is returned, following
+     *         the https://datatracker.ietf.org/doc/html/rfc5322#section-3.6.2 recommendation. If no reply-to address has been
+     *         set, it returns {@code null}.
      */
     public String getReplyTo() {
-        return replyTo;
+        if (replyTo == null || replyTo.isEmpty()) {
+            return null;
+        }
+        return String.join(",", replyTo);
+    }
+
+    /**
+     * Adds a reply-to address.
+     *
+     * @param replyTo the address to use as reply-to. Must be a valid email address.
+     * @return the current {@link Mail}
+     * @see #setReplyTo(String)
+     */
+    public Mail addReplyTo(String replyTo) {
+        this.replyTo.add(replyTo);
+        return this;
     }
 
     /**
      * Sets the reply-to address.
      *
      * @param replyTo the address to use as reply-to. Must be a valid email address.
      * @return the current {@link Mail}
+     * @see #setReplyTo(String[])
      */
     public Mail setReplyTo(String replyTo) {
-        this.replyTo = replyTo;
+        this.replyTo.clear();
+        this.replyTo.add(replyTo);
+        return this;
+    }
+
+    /**
+     * Sets the reply-to addresses.
+     *
+     * @param replyTo the addresses to use as reply-to. Must contain valid email addresses, must contain at least
+     *        one address.
+     * @return the current {@link Mail}
+     */
+    public Mail setReplyTo(String... replyTo) {
+        this.replyTo.clear();
+        Collections.addAll(this.replyTo, replyTo);
         return this;
     }
 
@@ -436,7 +468,8 @@ public Mail addAttachment(String name, byte[] data, String contentType, String d
      * @param disposition the disposition of the attachment
      * @return the current {@link Mail}
      */
-    public Mail addAttachment(String name, Publisher<Byte> data, String contentType, String description, String disposition) {
+    public Mail addAttachment(String name, Publisher<Byte> data, String contentType, String description,
+            String disposition) {
         this.attachments.add(new Attachment(name, data, contentType, description, disposition));
         return this;
     }

extensions/mailer/runtime/src/main/java/io/quarkus/mailer/MailTemplate.java

@@ -48,6 +48,8 @@ interface MailTemplateInstance {
 
         MailTemplateInstance replyTo(String replyTo);
 
+        MailTemplateInstance replyTo(String... replyTo);
+
         MailTemplateInstance bounceAddress(String bounceAddress);
 
         MailTemplateInstance addInlineAttachment(String name, File file, String contentType, String contentId);

extensions/mailer/runtime/src/main/java/io/quarkus/mailer/runtime/MailTemplateInstanceImpl.java

@@ -73,6 +73,12 @@ public MailTemplateInstance replyTo(String replyTo) {
         return this;
     }
 
+    @Override
+    public MailTemplateInstance replyTo(String... replyTo) {
+        this.mail.setReplyTo(replyTo);
+        return this;
+    }
+
     @Override
     public MailTemplateInstance bounceAddress(String bounceAddress) {
         this.mail.setBounceAddress(bounceAddress);

extensions/mailer/runtime/src/main/java/io/quarkus/mailer/runtime/MutinyMailerImpl.java

@@ -105,6 +105,7 @@ private Uni<MailMessage> toMailMessage(Mail mail) {
         message.setHtml(mail.getHtml());
         message.setHeaders(toMultimap(mail.getHeaders()));
         if (mail.getReplyTo() != null) {
+            // getReplyTo produces the comma-separated list.
             message.addHeader("Reply-To", mail.getReplyTo());
         }
 

extensions/mailer/runtime/src/test/java/io/quarkus/mailer/MailTest.java

@@ -171,4 +171,32 @@ void testHeaders() {
         assertThat(mail.getHeaders()).isEmpty();
     }
 
+    @Test
+    void testMultipleReplyTo() {
+        Mail mail = new Mail().addTo(TO_ADDRESS).setSubject("test").setText(BEGINNING)
+                .setFrom("from@quarkus.io")
+                .setReplyTo("reply-to@quarkus.io", "another@quarkus.io")
+                .setBounceAddress("bounce@quarkus.io");
+        assertThat(mail.getTo()).containsExactly(TO_ADDRESS);
+        assertThat(mail.getSubject()).isEqualTo("test");
+        assertThat(mail.getText()).isEqualTo(BEGINNING);
+        assertThat(mail.getHtml()).isNull();
+        assertThat(mail.getFrom()).isEqualTo("from@quarkus.io");
+        assertThat(mail.getReplyTo()).isEqualTo("reply-to@quarkus.io,another@quarkus.io");
+        assertThat(mail.getBounceAddress()).isEqualTo("bounce@quarkus.io");
+
+        mail = new Mail().addTo(TO_ADDRESS).setSubject("test").setText(BEGINNING)
+                .setFrom("from@quarkus.io")
+                .addReplyTo("another@quarkus.io")
+                .addReplyTo("reply-to@quarkus.io")
+                .setBounceAddress("bounce@quarkus.io");
+        assertThat(mail.getTo()).containsExactly(TO_ADDRESS);
+        assertThat(mail.getSubject()).isEqualTo("test");
+        assertThat(mail.getText()).isEqualTo(BEGINNING);
+        assertThat(mail.getHtml()).isNull();
+        assertThat(mail.getFrom()).isEqualTo("from@quarkus.io");
+        assertThat(mail.getReplyTo()).isEqualTo("another@quarkus.io,reply-to@quarkus.io");
+        assertThat(mail.getBounceAddress()).isEqualTo("bounce@quarkus.io");
+    }
+
 }

extensions/mailer/runtime/src/test/java/io/quarkus/mailer/runtime/MailerImplTest.java

@@ -165,7 +165,7 @@ public Byte next() {
 
     @Test
     void testInlineAttachment() throws MessagingException, IOException {
-        String cid = UUID.randomUUID().toString() + "@acme";
+        String cid = UUID.randomUUID() + "@acme";
         mailer.send(Mail.withHtml(TO, "Test", "testInlineAttachment")
                 .addInlineAttachment("inline.txt", "my inlined text".getBytes(StandardCharsets.UTF_8), TEXT_CONTENT_TYPE, cid))
                 .await().indefinitely();
@@ -210,6 +210,19 @@ void testReplyToHeaderIsSet() throws MessagingException {
         assertThat(msg.getReplyTo()).containsExactly(InternetAddress.parse("reply-to@quarkus.io"));
     }
 
+    @Test
+    void testMultipleReplyToHeaderIsSet() throws MessagingException {
+        mailer.send(Mail.withText(TO, "Test", "testHeaders")
+                .setReplyTo("reply-to@quarkus.io", "another@quarkus.io"))
+                .await().indefinitely();
+        assertThat(wiser.getMessages()).hasSize(1);
+        WiserMessage actual = wiser.getMessages().get(0);
+        MimeMessage msg = actual.getMimeMessage();
+        assertThat(msg.getHeader("Reply-To")).containsExactly("reply-to@quarkus.io,another@quarkus.io");
+        assertThat(msg.getReplyTo()).hasSize(2).contains(InternetAddress.parse("reply-to@quarkus.io"))
+                .contains(InternetAddress.parse("another@quarkus.io"));
+    }
+
     private String getContent(WiserMessage msg) {
         try {
             Object content = msg.getMimeMessage().getContent();
@@ -279,24 +292,4 @@ private String getTextFromMimeMultipart(
         return result.toString();
     }
 
-    private List<String> getContentTypesFromMimeMultipart(
-            MimeMultipart mimeMultipart) throws MessagingException, IOException {
-        List<String> types = new ArrayList<>();
-        int count = mimeMultipart.getCount();
-        for (int i = 0; i < count; i++) {
-            BodyPart bodyPart = mimeMultipart.getBodyPart(i);
-            if (bodyPart.getContent() instanceof MimeMultipart) {
-                types.addAll(getContentTypesFromMimeMultipart((MimeMultipart) bodyPart.getContent()));
-            } else {
-                types.add(bodyPart.getContentType());
-            }
-        }
-        return types;
-    }
-
-    private List<String> getContentTypesFromMimeMultipart(
-            String content) throws MessagingException, IOException {
-        return Collections.singletonList(content);
-    }
-
 }