diff --git a/tests/common/server.nix b/tests/common/server.nix
index ff60d5d..34476df 100644
--- a/tests/common/server.nix
+++ b/tests/common/server.nix
@@ -1,4 +1,4 @@
-{...}: {
+{lib, ...}: {
   imports = [./../../mailsystem];
   config = {
     virtualisation.memorySize = 1024;
@@ -6,5 +6,12 @@
       enable = true;
       certificateScheme = "selfsigned";
     };
+
+    # Enable more verbose logging (required for, e.g., sieve testing)
+    services.dovecot2.extraConfig = lib.mkAfter ''
+      mail_debug = yes
+      auth_debug = yes
+      verbose_ssl = yes
+    '';
   };
 }
diff --git a/tests/rspamd.nix b/tests/rspamd.nix
index ef8e6ea..eb71ed6 100644
--- a/tests/rspamd.nix
+++ b/tests/rspamd.nix
@@ -152,8 +152,11 @@ in
 
           client.succeed("${test-mark-spam "normal2"} >&2")
           server.wait_until_succeeds("journalctl -u dovecot2 | grep -i learn-spam.sh >&2")
+          server.fail("journalctl -u dovecot2 | grep -i learn-spam.sh | grep -i error >&2")
+
           client.succeed("${test-mark-ham "normal2"} >&2")
           server.wait_until_succeeds("journalctl -u dovecot2 | grep -i learn-ham.sh >&2")
+          server.fail("journalctl -u dovecot2 | grep -i learn-ham.sh | grep -i error >&2")
 
       with subtest("dkim signing"):
           client.succeed("${sendMail "normal2" "" accounts."normal".address ''