Index: src/groovy/org/grails/mail/MailMessageBuilder.groovy
===================================================================
--- src/groovy/org/grails/mail/MailMessageBuilder.groovy	(Revision 54429)
+++ src/groovy/org/grails/mail/MailMessageBuilder.groovy	(Arbeitskopie)
@@ -79,7 +79,7 @@
 	void attachBytes(String fileName, String contentType, byte[] bytes) {
 		def msg = getMessage()
 		if(msg instanceof MimeMailMessage) {
-			MimeMessageHelper message = new MimeMessageHelper(getMessage(), true, "UTF-8");
+			MimeMessageHelper message = new MimeMessageHelper(msg.mimeMessage, true, "UTF-8");
 		    message.addAttachment(fileName, new ByteArrayResource(bytes), contentType)			
 		}
 		else {
Index: test/unit/org/grails/mail/MailMessageBuilderTests.groovy
===================================================================
--- test/unit/org/grails/mail/MailMessageBuilderTests.groovy	(Revision 54429)
+++ test/unit/org/grails/mail/MailMessageBuilderTests.groovy	(Arbeitskopie)
@@ -21,6 +21,7 @@
 import org.codehaus.groovy.grails.commons.ConfigurationHolder
 import org.springframework.mail.MailSender
 import org.springframework.mail.javamail.JavaMailSender
+import javax.mail.internet.MimeMultipart
 
 /**
  * Test case for {@link MailMessageBuilder}.
@@ -127,6 +128,22 @@
         }
     }
 
+    void testAttachment() {
+        processDsl {
+            to "fred@g2one.com"
+            subject "Hello Fred"
+            body 'How are you?'
+            attachBytes "dummy.bin", "application/binary", "abcdef".bytes
+        }
+        def msg = testBuilder.createMessage().mimeMessage
+        assertTrue msg.content instanceof MimeMultipart
+        assertEquals 2, msg.content.count
+
+        def attachment = msg.content.getBodyPart(1)
+        assertEquals "abcdef", attachment.content.text
+        assertEquals "dummy.bin", attachment.fileName
+    }
+
     private List to(MimeMessage msg) {
         msg.getRecipients(Message.RecipientType.TO)*.toString()
     }