fix: improve way of populating smtp key/cert to avoid TypeError in py…

…>=12

flask_mailman/backends/smtp.py

@@ -2,6 +2,7 @@
 import smtplib
 import ssl
 import threading
+from werkzeug.utils import cached_property
 
 from flask_mailman.backends.base import BaseEmailBackend
 from flask_mailman.message import sanitize_address
@@ -48,6 +49,15 @@ def __init__(
     def connection_class(self):
         return smtplib.SMTP_SSL if self.use_ssl else smtplib.SMTP
 
+    @cached_property
+    def ssl_context(self):
+        if self.ssl_certfile or self.ssl_keyfile:
+            ssl_context = ssl.SSLContext(protocol=ssl.PROTOCOL_TLS_CLIENT)
+            ssl_context.load_cert_chain(self.ssl_certfile, self.ssl_keyfile)
+            return ssl_context
+        else:
+            return ssl.create_default_context()
+
     def open(self):
         """
         Ensure an open connection to the email server. Return whether or not a
@@ -64,12 +74,7 @@ def open(self):
         if self.timeout is not None:
             connection_params['timeout'] = self.timeout
         if self.use_ssl:
-            connection_params.update(
-                {
-                    'keyfile': self.ssl_keyfile,
-                    'certfile': self.ssl_certfile,
-                }
-            )
+            connection_params["context"] = self.ssl_context
         try:
             self.connection = self.connection_class(self.host, self.port, **connection_params)
 

tests/test_backend.py

@@ -2,6 +2,7 @@
 from email.utils import parseaddr
 import os
 import socket
+from ssl import SSLError
 import tempfile
 import pytest
 
@@ -341,6 +342,15 @@ def test_email_tls_attempts_starttls(self):
                 with backend:
                     pass
 
+    def test_email_ssl_attempts_ssl_connection(self):
+        with SmtpdContext(self.app.extensions['mailman']):
+            self.app.extensions['mailman'].use_ssl = True
+            backend = smtp.EmailBackend()
+            self.assertTrue(backend.use_ssl)
+            with self.assertRaises(SSLError):
+                with backend:
+                    pass
+
     def test_connection_timeout_default(self):
         """The connection's timeout value is None by default."""
         self.app.extensions['mailman'].backend = "smtp"