diff --git a/swh/web/auth/mailmap.py b/swh/web/auth/mailmap.py
--- a/swh/web/auth/mailmap.py
+++ b/swh/web/auth/mailmap.py
@@ -57,8 +57,11 @@
         UserMailmap.objects.create(
             user_id=str(request.user.id), from_email=from_email, **request.data
         )
-    except IntegrityError:
-        return HttpResponseBadRequest("This 'from_email' already exists.")
+    except IntegrityError as e:
+        if "user_mailmap_from_email_key" in e.args[0]:
+            return HttpResponseBadRequest("This 'from_email' already exists.")
+        else:
+            raise
 
     event.successful = True
     event.save()