1 files changed, 5 insertions, 1 deletions

diff --git a/src/mailman/chains/headers.py b/src/mailman/chains/headers.py
index 70f1da587..5698740d3 100644
--- a/src/mailman/chains/headers.py
+++ b/src/mailman/chains/headers.py
@@ -96,7 +96,11 @@ class HeaderMatchRule:
 
     def check(self, mlist, msg, msgdata):
         """See `IRule`."""
-        for value in msg.get_all(self.header, []):
+        # Collect all the headers in all subparts.
+        headers = []
+        for p in msg.walk():
+            headers.extend(p.get_all(self.header, []))
+        for value in headers:
             if re.search(self.pattern, value, re.IGNORECASE):
                 return True
         return False