diff --git a/app.py b/app.py
index 7bac0e1..8671eff 100644
--- a/app.py
+++ b/app.py
@@ -150,14 +150,22 @@ def oidc_callback():
     if not OAUTH:
         abort(404)
     if request.args.get("error"):
-        return redirect(url_for("index", error=request.args["error"]))
+        return render_template("index.html", email_address=EMAIL_USERNAME, oauth=True, connected=False,
+                               error=request.args["error"]), 400
     try:
         OAUTH.finish(request.args.get("state", ""), request.args.get("code", ""))
     except OAuthError as e:
         logger.warning("Mailbox connect failed: %s", e)
-        return redirect(url_for("index", error=str(e)))
+        return render_template("index.html", email_address=EMAIL_USERNAME, oauth=True, connected=False,
+                               error=str(e)), 400
     logger.info("Collection mailbox %s connected via OAuth", EMAIL_USERNAME)
-    return redirect(url_for("index"))
+    # the browser session now belongs to the technical account, which forward_auth does not let in:
+    # confirm here instead of redirecting to the start page
+    return (
+        "<!doctype html><meta charset=utf-8><title>Connected</title>"
+        "<p>Collection mailbox connected. Close this private window and open the Unsubscriber again "
+        "in your normal browser.</p>"
+    )
 
 
 @app.route("/disconnect", methods=["POST"])
diff --git a/index.html b/index.html
index d8ba050..719dc11 100644
--- a/index.html
+++ b/index.html
@@ -19,8 +19,9 @@
         </form>
         {% endif %}
         {% else %}
-        <p>The collection mailbox is not connected yet. Open this page in a private window and sign in
-           as <strong>{{ email_address }}</strong> (technical account) – not with your own account.</p>
+        <p>The collection mailbox is not connected yet. In a private window: open this page, sign in with
+           <strong>your own account</strong>, click “Connect mailbox”, then sign in as
+           <strong>{{ email_address }}</strong> (technical account).</p>
         <form action="/connect" method="get">
             <button type="submit" class="btn-primary">Connect mailbox</button>
         </form>
diff --git a/tests/test_oauth.py b/tests/test_oauth.py
index d9c4298..d00212f 100644
--- a/tests/test_oauth.py
+++ b/tests/test_oauth.py
@@ -139,3 +139,30 @@ def test_index_shows_connect_when_not_connected(monkeypatch):
     monkeypatch.setattr(unsub, "OAUTH", FakeOAuth())
     html = unsub.app.test_client().get("/").get_data(as_text=True)
     assert 'action="/connect"' in html and 'action="/result"' not in html
+
+
+def test_callback_confirms_without_redirect(monkeypatch):
+    import app as unsub
+
+    class FakeOAuth:
+        def finish(self, state, code):
+            assert (state, code) == ("s", "c")
+
+    monkeypatch.setattr(unsub, "OAUTH", FakeOAuth())
+    r = unsub.app.test_client().get("/oidc/callback?state=s&code=c")
+    assert r.status_code == 200 and "connected" in r.get_data(as_text=True)
+
+
+def test_callback_error_is_shown(monkeypatch):
+    import app as unsub
+
+    class FakeOAuth:
+        def finish(self, state, code):
+            raise oauth.OAuthError("Signed in as philipp@example.org, expected unsubscribe-bot@example.org")
+
+        def connected(self):
+            return False
+
+    monkeypatch.setattr(unsub, "OAUTH", FakeOAuth())
+    r = unsub.app.test_client().get("/oidc/callback?state=s&code=c")
+    assert r.status_code == 400 and "expected unsubscribe-bot" in r.get_data(as_text=True)