Fix JMAP sorting order issues when emails lack receivedAt headers

CHANGELOG.md

@@ -13,6 +13,7 @@ This version includes **multiple breaking changes**. If you are upgrading from v
 ## Fixed
 - JMAP:
   - Invalid `receivedAt` headers after importing (#2939).
+  - Sorting order issues when emails lack `receivedAt` headers.
 - Reverse proxy issues.
 - OSS builds.
 - DNS Updater:

crates/store/src/search/local.rs

@@ -204,11 +204,14 @@ impl QueryResults {
                             !set.contains(*b) as u32,
                             *ascending,
                         ),
-                        SearchComparator::SortedSet { set, ascending } => (
-                            *set.get(a).unwrap_or(&u32::MAX),
-                            *set.get(b).unwrap_or(&u32::MAX),
-                            *ascending,
-                        ),
+                        SearchComparator::SortedSet { set, ascending } => {
+                            let missing = if *ascending { u32::MAX } else { 0 };
+                            (
+                                *set.get(a).unwrap_or(&missing),
+                                *set.get(b).unwrap_or(&missing),
+                                *ascending,
+                            )
+                        }
                         SearchComparator::Field { .. } => continue,
                     };