smtp transport self signed certificate error: NotificationTransportError: [SSL: CERTIFICATE_VERIFY_FAILED]

[bestrocker221]

Describe the bug
SMTP stopped working (since end of April) and the error shown by testing the email send is the following:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/manage.py", line 46, in <module>
    execute_from_command_line(sys.argv)
  File "/ak-root/venv/lib/python3.12/site-packages/django/core/management/__init__.py", line 442, in execute_from_command_line
    utility.execute()
  File "/ak-root/venv/lib/python3.12/site-packages/django/core/management/__init__.py", line 436, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/ak-root/venv/lib/python3.12/site-packages/django/core/management/base.py", line 413, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/ak-root/venv/lib/python3.12/site-packages/django/core/management/base.py", line 459, in execute
    output = self.handle(*args, **options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/authentik/tenants/management/__init__.py", line 38, in handle
    self.handle_per_tenant(*args, **options)
  File "/ak-root/venv/lib/python3.12/site-packages/django/core/management/base.py", line 107, in wrapper
    res = handle_func(*args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/authentik/stages/email/management/commands/test_email.py", line 38, in handle_per_tenant
    send_mail(message.__dict__, stage.pk)
  File "/ak-root/venv/lib/python3.12/site-packages/celery/local.py", line 182, in __call__
    return self._get_current_object()(*a, **kw)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/ak-root/venv/lib/python3.12/site-packages/celery/app/task.py", line 411, in __call__
    return self.run(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/ak-root/venv/lib/python3.12/site-packages/celery/app/autoretry.py", line 60, in run
    ret = task.retry(exc=exc, **retry_kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/ak-root/venv/lib/python3.12/site-packages/celery/app/task.py", line 720, in retry
    raise_with_context(exc or Retry('Task can be retried', None))
  File "/ak-root/venv/lib/python3.12/site-packages/celery/app/autoretry.py", line 38, in run
    return task._orig_run(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/authentik/stages/email/tasks.py", line 106, in send_mail
    raise exc
  File "/authentik/stages/email/tasks.py", line 74, in send_mail
    backend.open()
  File "/ak-root/venv/lib/python3.12/site-packages/django/core/mail/backends/smtp.py", line 94, in open
    self.connection.starttls(context=self.ssl_context)
  File "/usr/local/lib/python3.12/smtplib.py", line 779, in starttls
    self.sock = context.wrap_socket(self.sock,
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/ssl.py", line 455, in wrap_socket
    return self.sslsocket_class._create(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/ssl.py", line 1042, in _create
    self.do_handshake()
  File "/usr/local/lib/python3.12/ssl.py", line 1320, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLCertVerificationError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: self-signed certificate (_ssl.c:1000)

To Reproduce
Configured SMTP via .env file were working for long time before. No changes have been done since then to email setup.
SMTP server is a big cloud vendor so there are no custom home made certificates involved.
Not sure how to debug further

Expected behavior
Email delivered correctly

Version and Deployment (please complete the following information):

• authentik version: 2024.4.1