diff --git a/ietf/utils/mail.py b/ietf/utils/mail.py
index e747c74778..4585fdb846 100644
--- a/ietf/utils/mail.py
+++ b/ietf/utils/mail.py
@@ -92,7 +92,17 @@ def send_smtp(msg, bcc=None):
     '''
     mark = time.time()
     add_headers(msg)
-    (fname, frm) = parseaddr(msg.get('From'))
+    # N.B. We have a disconnect with most of this code assuming a From header value will only
+    # have one address.
+    # The frm computed here is only used as the envelope from. 
+    # Previous code simply ran `parseaddr(msg.get('From'))`, getting lucky if the string returned
+    # from the get had more than one address in it. Python 3.9.20 changes the behavior of parseaddr
+    # and that erroneous use of the function no longer gets lucky.
+    # For the short term, to match behavior to date as closely as possible, if we get a message
+    # that has multiple addresses in the From header, we will use the first for the envelope from
+    from_tuples = getaddresses(msg.get_all('From', [settings.DEFAULT_FROM_EMAIL]))
+    assertion('len(from_tuples)==1', note=f"send_smtp received multiple From addresses: {from_tuples}")
+    _ , frm = from_tuples[0]
     addrlist = msg.get_all('To') + msg.get_all('Cc', [])
     if bcc:
         addrlist += [bcc]
@@ -446,6 +456,8 @@ def parse_preformatted(preformatted, extra=None, override=None):
         values = msg.get_all(key, [])
         if values:
             values = getaddresses(values)
+            if key=='From':
+                assertion('len(values)<2', note=f'parse_preformatted is constructing a From with multiple values: {values}')
             del msg[key]
             msg[key] = ',\n    '.join(formataddr(v) for v in values)
     for key in ['Subject', ]:
diff --git a/ietf/utils/tests.py b/ietf/utils/tests.py
index d435583e89..decdd778d9 100644
--- a/ietf/utils/tests.py
+++ b/ietf/utils/tests.py
@@ -53,7 +53,7 @@ class SendingMail(TestCase):
 
     def test_send_mail_preformatted(self):
         msg = """To: to1@example.com, to2@example.com
-From: from1@ietf.org, from2@ietf.org
+From: from1@ietf.org
 Cc: cc1@example.com, cc2@example.com
 Bcc: bcc1@example.com, bcc2@example.com
 Subject: subject
@@ -63,7 +63,7 @@ def test_send_mail_preformatted(self):
         send_mail_preformatted(None, msg, {}, {})
         recv = outbox[-1]
         self.assertSameEmail(recv['To'], '<to1@example.com>, <to2@example.com>')
-        self.assertSameEmail(recv['From'], 'from1@ietf.org, from2@ietf.org')
+        self.assertSameEmail(recv['From'], 'from1@ietf.org')
         self.assertSameEmail(recv['Cc'], 'cc1@example.com, cc2@example.com')
         self.assertSameEmail(recv['Bcc'], None)
         self.assertEqual(recv['Subject'], 'subject')
@@ -71,14 +71,14 @@ def test_send_mail_preformatted(self):
 
         override = {
             'To': 'oto1@example.net, oto2@example.net',
-            'From': 'ofrom1@ietf.org, ofrom2@ietf.org',
+            'From': 'ofrom1@ietf.org',
             'Cc': 'occ1@example.net, occ2@example.net',
             'Subject': 'osubject',
         }
         send_mail_preformatted(request=None, preformatted=msg, extra={}, override=override)
         recv = outbox[-1]
         self.assertSameEmail(recv['To'], '<oto1@example.net>, <oto2@example.net>')
-        self.assertSameEmail(recv['From'], 'ofrom1@ietf.org, ofrom2@ietf.org')
+        self.assertSameEmail(recv['From'], 'ofrom1@ietf.org')
         self.assertSameEmail(recv['Cc'], 'occ1@example.net, occ2@example.net')
         self.assertSameEmail(recv['Bcc'], None)
         self.assertEqual(recv['Subject'], 'osubject')
@@ -86,14 +86,14 @@ def test_send_mail_preformatted(self):
 
         override = {
             'To': ['<oto1@example.net>', 'oto2@example.net'],
-            'From': ['<ofrom1@ietf.org>', 'ofrom2@ietf.org'],
+            'From': ['<ofrom1@ietf.org>'],
             'Cc': ['<occ1@example.net>', 'occ2@example.net'],
             'Subject': 'osubject',
         }
         send_mail_preformatted(request=None, preformatted=msg, extra={}, override=override)
         recv = outbox[-1]
         self.assertSameEmail(recv['To'], '<oto1@example.net>, <oto2@example.net>')
-        self.assertSameEmail(recv['From'], '<ofrom1@ietf.org>, ofrom2@ietf.org')
+        self.assertSameEmail(recv['From'], '<ofrom1@ietf.org>')
         self.assertSameEmail(recv['Cc'], '<occ1@example.net>, occ2@example.net')
         self.assertSameEmail(recv['Bcc'], None)
         self.assertEqual(recv['Subject'], 'osubject')