[FIX][IMP] mail: check for rcptto when finding destination aliases

When a new answer comes in a thread the mailgateway finds if the recipients
are linked to existing aliases. This allows notably to check if the author
can effectively contact this alias. Previously only the To was checked.
However we cannot ensure the recipient is contained in To as it could be
in Delivered-To for example. We now check for all possible recipients.

addons/mail/models/mail_thread.py

@@ -1032,7 +1032,7 @@ class MailThread(models.AbstractModel):
             if mail_messages:
                 model, thread_id = mail_messages.model, mail_messages.res_id
                 if not reply_private:  # TDE note: not sure why private mode as no alias search, copying existing behavior
-                    dest_aliases = Alias.search([('alias_name', '=', email_to_localpart)], limit=1)
+                    dest_aliases = Alias.search([('alias_name', 'in', rcpt_tos_localparts)], limit=1)
 
                 # TDE Note: compat mode = without context key, why ? because
                 route = self.message_route_verify(