diff --git a/Lib/email/_parseaddr.py b/Lib/email/_parseaddr.py
index e311948cb09a7d6..29718957a68a9be 100644
--- a/Lib/email/_parseaddr.py
+++ b/Lib/email/_parseaddr.py
@@ -307,7 +307,7 @@ def getaddress(self):
                 if self.pos < fieldlen and self.field[self.pos] == ';':
                     self.pos += 1
                     break
-                returnlist = returnlist + self.getaddress()
+                returnlist.extend(self.getaddress())
 
         elif self.field[self.pos] == '<':
             # Address is a phrase then a route addr
diff --git a/Misc/NEWS.d/next/Library/2026-10-20-00-00-00.gh-issue-159739.35942a.rst b/Misc/NEWS.d/next/Library/2026-10-20-00-00-00.gh-issue-159739.35942a.rst
new file mode 100644
index 000000000000000..548ac837589f078
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-10-20-00-00-00.gh-issue-159739.35942a.rst
@@ -0,0 +1 @@
+Improve performance when parsing email address groups with many members.