[FIX] base: always send HELO when connecting SMTP

smtplib.SMTP API calls such as .sendmail() or .login() make sure on
their first line that this command is sent, by calling
.ehlo_or_helo_if_needed().

However, test_smtp_connection() does not use SMTP.sendmail() to simulate
sending email, or the email would really be sent.
Instead it uses the low-level API SMTP.mail() which does not make sure
that HELO was sent.

The connection test could be fixed by ensuring that this command was
sent to the server in the test method. However, this could lead to
inconsistent cases where the connection test passes whereas another
usage in the code fails because the command was not sent.
For example, someone could use the low-level API for some reason.

EHLO could have already been sent because if authentication is enabled
smtplib.SMTP.login() calls ehlo_or_helo_if_needed(). Therefore it is
correct to call it ourselves at the end of our connect() method.

STARTTLS sends a first EHLO, negociates the encryption, and leaves the
state without the second EHLO, which should still be sent to the server,
as stated by RFC 3207, in section "4.2 Result of the STARTTLS Command".
https://www.ietf.org/rfc/rfc3207.txt

closes odoo/odoo#34550

Signed-off-by: Julien Legros (jle) <jle@odoo.com>

odoo/addons/base/models/ir_mail_server.py

@@ -277,6 +277,11 @@ class IrMailServer(models.Model):
             smtp_user = pycompat.to_native(ustr(smtp_user))
             smtp_password = pycompat.to_native(ustr(smtp_password))
             connection.login(smtp_user, smtp_password)
+
+        # Some methods of SMTP don't check whether EHLO/HELO was sent.
+        # Anyway, as it may have been sent by login(), all subsequent usages should consider this command as sent.
+        connection.ehlo_or_helo_if_needed()
+
         return connection
 
     def build_email(self, email_from, email_to, subject, body, email_cc=None, email_bcc=None, reply_to=False,