diff --git a/CHANGELOG.md b/CHANGELOG.md
index c18c1748..73156dd1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@ If you are upgrading from v0.16.x, replace the binary (or run `docker pull`). If
 - MTA: 
   - Sub-addressing with external directories returns `550 Mailbox not found`.
   - Disabled aliases continue receiving messages.
+- Make `SieveSystemInterpreter.defaultReturnPath` and `MtaQueueQuota.match` optional expressions.
 
 ## [0.16.7] - 2026-05-28
 
diff --git a/crates/registry/src/schema/structs_impl.rs b/crates/registry/src/schema/structs_impl.rs
index 7d797331..27db8905 100644
--- a/crates/registry/src/schema/structs_impl.rs
+++ b/crates/registry/src/schema/structs_impl.rs
@@ -27038,7 +27038,9 @@ impl ObjectImpl for MtaQueueQuota {
             errors.push(ValidationError::min_items(Property::Key, 1));
         }
         let value = &self.match_;
-        value.validate(errors);
+        if !value.match_.is_empty() || !value.else_.is_empty() {
+            value.validate(errors);
+        }
         if let Some(value) = &self.messages {
             if *value < 1 {
                 errors.push(ValidationError::min_value(Property::Messages, 1));
@@ -35218,7 +35220,9 @@ impl ObjectImpl for SieveSystemInterpreter {
             }
         }
         let value = &self.default_return_path;
-        value.validate(errors);
+        if !value.match_.is_empty() || !value.else_.is_empty() {
+            value.validate(errors);
+        }
         let value = &self.dkim_sign_domain;
         value.validate(errors);
         let value = &self.max_cpu_cycles;