[FIX] mass_mailing: allow multiple recipients in mailing

Commit 0cd656b5af improved onboarding of mass mailing application. Notably
mailing domain computation has been improved. However rewriting has not been
done correctly as there were strange formatting and encoding. This commit
fixes the issue and correctly uses a list to format a domain like expected.

This commit is related to task Id 1831211. Closes #23883 .

addons/mass_mailing/models/mass_mailing.py

@@ -518,20 +518,20 @@ class MassMailing(models.Model):
 
     @api.onchange('mailing_model_id', 'contact_list_ids')
     def _onchange_model_and_list(self):
-        str_tuples = ""
+        mailing_domain = []
         if self.mailing_model_name:
             if self.mailing_model_name == 'mail.mass_mailing.list':
                 if self.contact_list_ids:
-                    str_tuples += "('list_ids', 'in', {}),".format(','.join(str(id) for id in self.contact_list_ids.ids))
+                    mailing_domain.append(('list_ids', 'in', self.contact_list_ids.ids))
                 else:
-                    str_tuples += "(0, '=', 1),"
+                    mailing_domain.append((0, '=', 1))
             elif self.mailing_model_name == 'res.partner':
-                str_tuples += "('customer', '=', True),"
+                mailing_domain.append(('customer', '=', True))
             elif 'opt_out' in self.env[self.mailing_model_name]._fields and not self.mailing_domain:
-                str_tuples += "('opt_out', '=', False),"
+                mailing_domain.append(('opt_out', '=', False))
         else:
-            str_tuples += "(0, '=', 1),"
-        self.mailing_domain = "[{}]".format(str_tuples)
+            mailing_domain.append((0, '=', 1))
+        self.mailing_domain = repr(mailing_domain)
         self.body_html = "on_change_model_and_list"
 
     #------------------------------------------------------