diff --git a/swh/vault/api/server.py b/swh/vault/api/server.py
--- a/swh/vault/api/server.py
+++ b/swh/vault/api/server.py
@@ -74,14 +74,7 @@
     vcfg.update(vcfg.get("args", {}))
 
     # Default to top-level value if any
-    if "cache" not in vcfg:
-        vcfg["cache"] = cfg.get("cache")
-    if "storage" not in vcfg:
-        vcfg["storage"] = cfg.get("storage")
-    if "scheduler" not in vcfg:
-        vcfg["scheduler"] = cfg.get("scheduler")
-    if "client_max_size" not in vcfg:
-        vcfg["client_max_size"] = cfg.get("client_max_size")
+    vcfg = {**cfg, **vcfg}
 
     for key in ("cache", "storage", "scheduler"):
         if not vcfg.get(key):
diff --git a/swh/vault/backend.py b/swh/vault/backend.py
--- a/swh/vault/backend.py
+++ b/swh/vault/backend.py
@@ -73,7 +73,7 @@
         self.cache = VaultCache(**config["cache"])
         self.scheduler = get_scheduler(**config["scheduler"])
         self.storage = get_storage(**config["storage"])
-        self.smtp_server = smtplib.SMTP()
+        self.smtp_server = smtplib.SMTP(**config.get("smtp", {}))
 
         db_conn = config["db"]
         self._pool = psycopg2.pool.ThreadedConnectionPool(
diff --git a/swh/vault/cookers/base.py b/swh/vault/cookers/base.py
--- a/swh/vault/cookers/base.py
+++ b/swh/vault/cookers/base.py
@@ -6,6 +6,7 @@
 import abc
 import io
 import logging
+import traceback
 from typing import ClassVar, Set
 
 from psycopg2.extensions import QueryCanceledError
@@ -141,10 +142,12 @@
             self.backend.set_progress(self.BUNDLE_TYPE, self.swhid, str(e))
         except Exception:
             self.backend.set_status(self.BUNDLE_TYPE, self.swhid, "failed")
+            tb = traceback.format_exc()
             self.backend.set_progress(
                 self.BUNDLE_TYPE,
                 self.swhid,
-                "Internal Server Error. This incident will be reported.",
+                f"Internal Server Error. This incident will be reported.\n"
+                f"The full error was:\n\n{tb}",
             )
             logging.exception("Bundle cooking failed.")
         else:
diff --git a/swh/vault/tests/test_cookers_base.py b/swh/vault/tests/test_cookers_base.py
--- a/swh/vault/tests/test_cookers_base.py
+++ b/swh/vault/tests/test_cookers_base.py
@@ -1,8 +1,9 @@
-# Copyright (C) 2018  The Software Heritage developers
+# Copyright (C) 2018-2021  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+import textwrap
 from unittest.mock import MagicMock
 
 from swh.model.identifiers import CoreSWHID
@@ -56,7 +57,16 @@
     cooker.backend.put_bundle.assert_not_called()
 
     cooker.backend.set_status.assert_called_with(TEST_BUNDLE_TYPE, TEST_SWHID, "failed")
-    assert "Nope" not in cooker.backend.set_progress.call_args[0][2]
+    assert cooker.backend.set_progress.call_args[0][2].startswith(
+        textwrap.dedent(
+            """\
+            Internal Server Error. This incident will be reported.
+            The full error was:
+
+            Traceback (most recent call last):
+            """
+        )
+    )
     cooker.backend.send_notif.assert_called_with(TEST_BUNDLE_TYPE, TEST_SWHID)