mail: display user as unknown if it doesn't exist anymore (#13923)

welco/sources/mail/models.py

@@ -15,6 +15,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import re
+import requests
 import subprocess
 
 from django.conf import settings
@@ -98,7 +99,10 @@ class Mail(models.Model):
     def contact_name(self):
         if not self.contact_id:
             return ''
-        user_details = get_wcs_data('api/users/%s/' % self.contact_id)
+        try:
+            user_details = get_wcs_data('api/users/%s/' % self.contact_id)
+        except requests.HTTPError:
+            return _('unknown')
         return user_details.get('user_display_name')
 
     def html_note(self):