diff --git a/core/src/main/java/google/registry/groups/GmailClient.java b/core/src/main/java/google/registry/groups/GmailClient.java
index 569456784..be649570b 100644
--- a/core/src/main/java/google/registry/groups/GmailClient.java
+++ b/core/src/main/java/google/registry/groups/GmailClient.java
@@ -138,6 +138,7 @@ public final class GmailClient {
         BodyPart attachmentPart = new MimeBodyPart();
         attachmentPart.setContent(attachment.content(), attachment.contentType().toString());
         attachmentPart.setFileName(attachment.filename());
+        attachmentPart.setDisposition(MimeBodyPart.ATTACHMENT);
         multipart.addBodyPart(attachmentPart);
       }
       msg.addRecipients(RecipientType.BCC, toArray(emailMessage.bccs(), Address.class));
diff --git a/core/src/test/java/google/registry/groups/GmailClientTest.java b/core/src/test/java/google/registry/groups/GmailClientTest.java
index ea720ff37..1014602cd 100644
--- a/core/src/test/java/google/registry/groups/GmailClientTest.java
+++ b/core/src/test/java/google/registry/groups/GmailClientTest.java
@@ -138,6 +138,7 @@ public class GmailClientTest {
     assertThat(attachment.getContentType()).startsWith(CSV_UTF_8.toString());
     assertThat(attachment.getContentType()).endsWith("name=filename");
     assertThat(attachment.getContent()).isEqualTo("foo,bar\nbaz,qux");
+    assertThat(attachment.getDisposition()).isEqualTo("attachment");
   }
 
   @Test