[FIX] base: remove BCC header from outgoing emails to avoid leaking information

When sending emails SMTP server only requires an author, recipients and the
email to send. It does not make any modification of what is sent. It is
therefore possible that BCC content is sent.

BCC mean 'Blind Carbon Copy', the address in this field should be not send
in the header of the mail and must be removed, if not the address are visible
for all recipients.

Closes #21965 .

odoo/addons/base/ir/ir_mail_server.py

@@ -192,7 +192,7 @@ class IrMailServer(models.Model):
         """Returns a new SMTP connection to the give SMTP server, authenticated
            with ``user`` and ``password`` if provided, and encrypted as requested
            by the ``encryption`` parameter.
-        
+
            :param host: host or IP of SMTP server to connect to
            :param int port: SMTP port to connect to
            :param user: optional username to authenticate with
@@ -397,6 +397,7 @@ class IrMailServer(models.Model):
         email_to = message['To']
         email_cc = message['Cc']
         email_bcc = message['Bcc']
+        del message['Bcc']
 
         smtp_to_list = filter(None, tools.flatten(map(extract_rfc2822_addresses, [email_to, email_cc, email_bcc])))
         assert smtp_to_list, self.NO_VALID_RECIPIENT