diff --git a/musician/forms.py b/musician/forms.py
index 1302fb2..076898d 100644
--- a/musician/forms.py
+++ b/musician/forms.py
@@ -40,7 +40,7 @@ class MailForm(forms.Form):
 
         super().__init__(*args, **kwargs)
         self.fields['domain'].choices = [(d.url, d.name) for d in domains]
-        self.fields['mailboxes'].choices = [(m['url'], m['name']) for m in mailboxes]
+        self.fields['mailboxes'].choices = [(m.url, m.name) for m in mailboxes]
 
     def clean(self):
         cleaned_data = super().clean()
diff --git a/musician/models.py b/musician/models.py
index 9e62d51..a470a65 100644
--- a/musician/models.py
+++ b/musician/models.py
@@ -301,10 +301,12 @@ class Mailbox(OrchestraModel):
     description = _('Description details for mailbox page.')
     fields = ('name', 'filtering', 'addresses', 'active')
     param_defaults = {
+        'id': None,
         'name': None,
         'filtering': None,
         'is_active': True,
         'addresses': [],
+        'url': None,
     }
 
     @classmethod