diff --git a/app/email_utils.py b/app/email_utils.py
index 23ca2c2f..e4a8e2e3 100644
--- a/app/email_utils.py
+++ b/app/email_utils.py
@@ -304,6 +304,8 @@ def send_email(
     date_header = formatdate()
     msg[headers.DATE] = date_header
 
+    msg[headers.MIME_VERSION] = "1.0"
+
     if unsubscribe_link:
         add_or_replace_header(msg, headers.LIST_UNSUBSCRIBE, f"<{unsubscribe_link}>")
         if not unsubscribe_via_email: