diff --git a/contrib/testing/README.md b/contrib/testing/README.md
index b33be78..b6a4b60 100644
--- a/contrib/testing/README.md
+++ b/contrib/testing/README.md
@@ -32,8 +32,9 @@ one-off files in `/tmp`:
   configuration without committing a message.
 - `smtp-internal-normalization-check.py` sends only to the reserved
   `.invalid` namespace through trusted port 26, inspects the real Queue
-  routing envelope for ten sender-normalization cases, deletes every test
-  entry, and restores the exact SMTP configuration.
+  routing envelope for ten sender-normalization cases after atomically moving
+  each entry to the hold queue, deletes every test entry, and restores the
+  exact SMTP configuration.
 - `c-literal-length-check.py` audits manually sized string literals passed to
   Bongo connection I/O helpers and rejects lengths that include a trailing
   NUL, truncate a protocol line, or read past the literal.
diff --git a/contrib/testing/smtp-internal-normalization-check.py b/contrib/testing/smtp-internal-normalization-check.py
index 84c0812..666d4d2 100755
--- a/contrib/testing/smtp-internal-normalization-check.py
+++ b/contrib/testing/smtp-internal-normalization-check.py
@@ -239,7 +239,16 @@ def wait_envelope(baseline: set[str], expected_sender: str) -> str:
             raise NormalizationCheckError(
                 f"test created multiple Queue entries: {matches!r}")
         if matches:
-            queue_id = matches[0]
+            held = queue("hold", matches[0], check=False)
+            if held.returncode:
+                time.sleep(0.1)
+                continue
+            queue_id = held.stdout.strip()
+            if not QUEUE_ID.fullmatch(queue_id) or not queue_id.startswith(
+                "999-"
+            ):
+                raise NormalizationCheckError(
+                    f"invalid held Queue ID: {queue_id!r}")
             envelope = queue("show", queue_id, binary=True).stdout
             from_lines = [
                 line[1:].decode("utf-8", "strict").split()
@@ -347,7 +356,8 @@ def main() -> int:
     print(
         "SMTP-05 PASS "
         f"host={HOST}:{PORT} source={SOURCE} device={DEVICE} cases=10 "
-        "queue-envelope=yes fcrdns=unit-tested external-boundary=yes "
+        "queue-envelope=yes queue-held=yes fcrdns=unit-tested "
+        "external-boundary=yes "
         "internet-delivery=no restored=yes"
     )
     return 0